SLA AMMER R SEISMIC LANDSLID A E MOVEM MENT MODELED D USING G EARTH HQUAKE R RECORD DS USE ER GUID DE Ex xcerpted frrom U.S. Geological G Survey Meethods andd Techniquues 12-B1 By Randall W. Jibson, Elllen M. Ratthje, Matthhew W. Jibbson, and Y Yong W. Lee 2013 2 TABLE OF CONTENTS GENERAL INFORMATION ......................................................................................................... 3 Introduction ................................................................................................................................. 3 Strong-Motion Records ............................................................................................................... 3 File Formats................................................................................................................................. 4 Earthquake Data .......................................................................................................................... 4 Navigating the Program Pages .................................................................................................... 4 PROGRAM PAGES ....................................................................................................................... 5 Getting Started ......................................................................................................................... 5 Rigorous Analyses ................................................................................................................... 5 Simplified Empirical Models................................................................................................... 9 Manage/Add Records ............................................................................................................ 10 Utilities .................................................................................................................................. 14 DEFINITION OF TERMS ........................................................................................................... 15 REFERENCES CITED ................................................................................................................. 21 3 GENERAL INFORMATION Introduction SLAMMER (Seismic LAndslide Movement Modeled using Earthquake Records) is intended to facilitate performing a variety of sliding-block analyses to evaluate seismic slope performance. Programs include both rigorous and simplified rigid-block (Newmark) analysis, decoupled analysis of flexible sliding blocks, and fully coupled analysis of flexible sliding blocks. Rigorous analyses calculate displacement based on user-specified ground motions, while simplified analyses use empirical regression relationships to predict displacement based on ground motion parameters (such as peak ground acceleration). Several other programs are provided to assist users in determining important properties of strong-motion records and in preparing digital strong-motion files for use in the SLAMMER program. SLAMMER supersedes Jibson and Jibson (2003) and its predecessors. Users should be completely familiar with the details of each sliding-block method before using SLAMMER; Jibson (2011) provided a useful overview of various types of sliding-block analysis and how to apply them. The reference list contains references to all of the methods used, and users should familiarize themselves with the details of a specific method before applying it to a particular problem. The “Definition of Terms” section of the User Guide contains many useful definitions of terms used elsewhere. Users should check this section if they are uncertain about the meaning of any terms. Strong-Motion Records With only a few exceptions, the strong-motion records included in the imported program database were downloaded from the New Generation Attenuation (NGA) database, which is maintained by the Pacific Earthquake Engineering Research Center (PEER) at the University of California, Berkeley. Data about these records (station locations, source distances, earthquake locations and source mechanisms, site conditions, data sources, filtering, corrections) can be obtained from the NGA website: http://peer.berkeley.edu/nga/. Records from the 2001 Nisqually, Washington earthquake were obtained from the University of Washington. File names of strong-motion records correspond to “Record” names in the program. The names consist of an alpha-numeric station code, a hyphen, and a three-digit number denoting the horizontal directional component of the record. Station names are unique. Where possible, station names used in the NGA database were retained, but in some cases these names were not unique and were therefore changed. The record library contains only horizontal components because all of the sliding-block analyses use only horizontal motions. 4 File Formats The program will read text files containing numeric data in any numeric format. The data can be delimited by spaces, tabs, commas, or line feeds. Any header information must be removed from data files so that only acceleration values are contained in the file. Programs on the Utilities page allow users to remove header information from files to prepare them for use in this program. For files containing time/acceleration pairs, which must be run through the “Redigitize” utility in order to be imported into the program, the program assumes that the first value is a time value, the next value is the corresponding acceleration, and so on. Earthquake Data Earthquake Cape Mendocino, Calif. Chi-Chi, Taiwan Coalinga, Calif. Coyote Lake, Calif. Daly City, Calif. Duzce, Turkey Friuli, Italy Imperial Valley, Calif. Imperial Valley, Calif. Kern County, Calif. Kobe, Japan Kocaeli, Turkey Landers, Calif. Loma Prieta, Calif. Mammoth Lakes-1, Calif. Mammoth Lakes-2, Calif. Morgan Hill, Calif. North Palm Springs, Calif. Nahanni, Canada Nisqually, Wash. Northridge, Calif. Parkfield, Calif. San Fernando, Calif. Santa Barbara, Calif. Superstition Hills, Calif. Tabas, Iran Westmorland, Calif. Whittier Narrows, Calif. Date 25-Apr-1992 21-Sep-1999 2-May-1983 6-Aug-1979 22-Mar-1957 12-Nov-1999 6-May-1976 18-May-1940 15-Oct-1979 21-Jul-1952 17-Jan-1995 17-Aug-1999 28-Jun-1992 17-Oct-1989 25-May-1980 27-May-1980 24-Apr-1984 8-Jul-1986 23-Dec-1985 28-Feb-2001 17-Jan-1994 28-Jun-1966 9-Feb-1971 13-Aug-1978 23-Nov-1987 16-Sep-1978 26-Apr-1981 1-Oct-1987 Mag. 7.0 7.6 6.4 5.7 5.3 7.1 6.5 7.0 6.5 7.4 6.9 7.5 7.3 6.9 6.1 5.9 6.2 6.1 6.8 6.8 6.7 6.2 6.6 5.9 6.5 7.4 5.9 6.0 Focal Mechanism Reverse Oblique reverse Reverse Strike-slip Reverse Strike-slip Reverse Strike-slip Strike-slip Reverse Strike-slip Strike-slip Strike-slip Oblique reverse Oblique normal Strike-slip Strike-slip Oblique reverse Reverse Normal Reverse Strike-slip Reverse Oblique reverse Strike-slip Reverse Strike-slip Oblique reverse Lat. 40.3338 23.8603 36.2330 37.0845 37.6700 40.7746 46.3450 32.7601 32.6435 34.9767 34.5948 40.7270 34.2000 37.0407 37.6090 37.5060 37.3060 34.0000 62.1870 47.1525 34.2057 35.9550 34.4400 34.3987 33.0222 33.2150 33.1000 34.0493 Long. -124.2290 120.7995 -120.3100 -121.5050 -122.4800 31.1870 13.2400 -115.4160 -115.3090 -119.0330 135.0121 29.9900 -116.4300 -121.8830 -118.8460 -118.8260 -121.6950 -116.6120 -124.2430 -122.7197 -118.5540 -120.4980 -118.4100 -119.6810 -115.8310 57.3230 -115.6200 -118.0810 Depth (km) 9.6 6.8 4.6 9.6 8.0 10.0 5.1 8.8 10.0 16.0 17.9 15.0 7.0 17.5 9.0 14.0 8.5 11.0 8.0 52.4 17.5 10.0 13.0 12.7 9.0 5.8 2.3 14.6 Navigating the Program Pages Detailed descriptions of the contents of different program pages are available in the “Program Pages” section of the User Guide menu. Program tabs are arranged hierarchically to 5 lead users through the basic steps involved in conducting various types of analyses. The main set of tabs along the top of the program box includes the following: • Getting Started contains a title page with an overview of the program. • Rigorous Analyses contains a sequence of pages to lead users through a rigorous slidingblock analysis. Rigid-block, decoupled, and fully coupled analyses can be performed on these pages. • Simplified Empirical Models contains pages that allow users to conduct (1) various types of simplified rigid-block analyses, (2) flexible (coupled) analysis, (3) flexible/rigid unified analysis, and (4) estimation of probability of failure given a specified slidingblock displacement. • Manage/Add Records contains pages allowing users to (1) view or modify record properties, (2) graph records in either time or frequency domain, or (3) add earthquake records to the database. • Utilities contains programs designed to convert existing strong-motion files into different forms. • User Guide contains information for each of the program pages as well as definitions of terms used and references cited. PROGRAM PAGES Getting Started This page contains a brief overview of the program and its various pages (tabs). Rigorous Analyses Rigorous analysis calculates displacement based on user-specified ground motions. This page contains three tabs that are numbered as sequential steps to take users through a rigorous sliding-block analysis: (1) Select records, (2) Select analyses, and (3) Perform analyses and view results. Each of these tabs is explained below: Step 1: Select records. This page allows users to select which earthquake strong-motion records will be used in an analysis. Records can be selected in one of two ways, indicated by the two tabs on this page: (1) Search records by properties, or (2) Select individual records. Search records by properties. To search for records based on record properties, simply enter values into any of the search fields desired. Any number of search fields can be used concurrently in any search. For a given property, one or both of the fields can be used: to search a range of values, use both fields; to search for all records above or below a certain value, use only a single field. To search for a unique value, put the same value in both fields. See the “Definition of terms” section of the User Guide for definitions of the various properties listed, including the various definitions of distance. If users add records to the database and do not include some of these properties, those records will not be selected on a search of a property for which no data have been provided. When the desired search parameters have been specified, click the “Search for records” button. A message to the right of the search fields will indicate 6 when the search is completed and how many records matched the criteria. The records meeting the search criteria will appear in the “Records selected” list at the bottom of the page. This list also displays all of the properties of each record. Multiple searches can be conducted, and all new records identified in a given search will be added to the list. No duplicate records are allowed on the list; thus, if a search identifies a record that is already on the list, it is ignored. To clear the search fields between searches, click the “Clear all search fields” button. Select individual records. To search for records individually by name, click on the down arrow under the “Earthquake” heading. Select an earthquake from the list of earthquakes displayed. Then click the down arrow under “Record name” and select the desired record from the list. Click “Select record” to add that record to the “Records selected” list. For each earthquake, “Select all records” is displayed at the top of the Record list; use this option to select all records from a given earthquake. The “Records selected” list at the bottom of the page displays all of the properties of the earthquake records selected (units are the same as indicated in the search boxes at the top of the page). The table display can be toggled between displaying properties of specific records (for example, Arias intensity, duration, PGA, PGV, mean period, source distance) and properties of the station in general (for example, location, latitude and longitude, site classification). Records in the table can be sorted by any of the properties listed by selecting those properties in the primary and secondary “Sort by” boxes at the top of the table. Records can be sorted in any combination of ascending or descending order using the drop-down box next to the sort boxes. The last column on the right contains a check box that allows the user to indicate whether or not each record is to be included in the analysis. When records are added to the table, they are selected by default. All the records on the list can be selected or deselected by clicking on the buttons at the upper right corner of the list. Individual records can be selected or deselected by clicking the individual check box corresponding to that record. The “Clear table” button at the bottom removes all records from the table; the “Clear highlighted record(s)” button removes all highlighted records. “Group Manager” (bottom left) is used to save groups of records for future use. The Group Manager allows users to retrieve previously saved groups, to name and add new groups, and to delete groups. Groups of records with their associated properties can also be exported in a variety of formats; this allows users to export the information displayed in the table into a spreadsheet or other program if other types of analysis on record properties are desired. When all the desired records have been added to the table and selected, go to the next page by clicking on the “Go to Step 2: Select analyses” button at the bottom right or the “Step 2: Select analyses” tab on the top of the page. Step 2: Select analyses. This page requires the user to specify basic calculation parameters and the types of analyses to be performed. Choose analysis properties: The following analysis properties must be specified: 7 Units: Choose metric or English units for input parameters and analysis results. If properties on the bottom of the page have been input in one set of units, switching to a different set of units will cause the values in the input boxes to automatically convert to the specified set of units. Scaling: Selected records can be analyzed (1) unscaled, (2) scaled to a uniform PGA (specified in terms of g), or (3) scaled by a specified constant. Critical Acceleration: Critical (yield) acceleration is the threshold ground acceleration required to initiate landslide movement and is specified in terms of g, the acceleration of Earth’s gravity. Two choices are available for specifying critical acceleration. If “Constant” is selected, a single value is entered into the corresponding field; in this situation, the landslide critical acceleration remains constant throughout the analysis. If “Varies with displacement” is selected, the user can enter pairs of displacement/critical acceleration values to define a curve of varying critical acceleration as a function of displacement. Each successive value of displacement must be greater than the previous value. A value of “0” is locked into the upper left box, which indicates that the analysis begins at zero displacement. When the initial value of critical acceleration is added to the right-hand box in the first row, the “Enter” key must be used to save the value. Any number of points (paired values) can be input by clicking on the “Add row” button. Any empty rows must be deleted for the analysis to run. The program linearly interpolates critical-acceleration values between points. The critical acceleration remains constant at the last value specified when the last displacement specified is exceeded. Choose types of analysis: Any or all types of analysis can be performed simultaneously. Check the boxes next to the types of analysis desired. Rigid Block: This type of analysis can be conducted so as to allow only downslope displacement or to allow both upslope and downslope displacement. If the latter is selected, the thrust angle of the potential landslide block must be specified. Coupled and Decoupled: Conducting coupled and (or) decoupled analysis of a flexible sliding block requires specifying several slope properties: (1) Height, the maximum vertical thickness of the potential sliding block, (2) the shear-wave velocity of the material above the slip surface, (3) the shear-wave velocity of the material below the slip surface (commonly taken as rock), (4) the damping ratio of the material within the sliding block, and (5) the reference strain used to define the nonlinear modulus reduction and damping curves of the soil within the sliding block (default is 0.05 percent). The type of soil model, linear elastic or equivalent linear, also must be specified. The equivalent linear analysis is the most complex and requires the greatest computing time. When all parameters have been entered on this page, click on “Go to Step 3: Perform analyses and view results” at the lower right, or click the “Step 3: Perform analyses and view results” tab on the top of the page. 8 Step 3: Perform analyses and view results. Results can be displayed to any number of decimals specified in the input box at the upper left; the default is 1. When the “Perform analyses” button is clicked, the selected records will be analyzed, and the results will be displayed in the table. Processing time depends on the number and size of the records selected and the types of analyses being performed. An indicator bar shows the progress as each record is analyzed. Equivalent linear analysis is the most computationally intensive and can take long periods of time for large records. The results table shows the earthquake name, the record name, and calculated displacements for the types of analysis selected. Three displacements are shown for each type of analysis and for each record analyzed: (1) normal polarity (the “top” or positive accelerations), (2) inverse polarity (the “bottom” or negative accelerations), and (3) the average of the two polarities. All displacements are given in centimeters if metric units were specified or in inches if English units were specified. At the bottom of the table, the mean, median, and standard deviation (based on population) of the average displacements are shown. Clicking the “Display dynamic response parameters” box at the upper right provides information about the dynamic response induced within the sliding mass for decoupled and coupled analysis. When clicked, the results table will display the maximum seismic coefficient induced by the earthquake motion (kmax), the shear-wave velocity (Vs), and damping for each of the records analyzed. Vs and damping represent the properties of the sliding mass used in the dynamic response analysis. When performing equivalent-linear analysis these values will be different than those input in Step 2 because of the nonlinear response of the sliding mass. Click on “Clear output” in the upper right part of the page to clear the currently displayed results and any corresponding plots. At the bottom of the page, three tabs allow graphing or saving the data from the Results table: Graph Displacements. Plots showing time histories of displacements can be generated. Select the analyses whose results are to be graphed and the desired polarity (average values cannot be graphed) and click “Plot displacements versus time.” Results from any combination of analyses can be plotted together. Right clicking on the resulting plot box allows the user to customize the appearance of the plot, save it, print it, or zoom in or out. Checking the “Display explanation” box will display an explanation keying colors of curves to specific earthquake records. There are a limited number of colors available for plotting, and so plots having large numbers of records will have duplicate colors for some records. Plotting displacements for large numbers of records makes plotting labels infeasible and can take several seconds; during this time the plot window will display a plain gray background until the plot appears. Graph Histogram. Histograms of the results of each type of analysis can be plotted. Results from only one type of analysis can be plotted on a single histogram. Average, normal, or inverse polarities can be plotted. Any number of histogram bins can be specified; the default is 10. Right clicking on the resulting plot box allows the user to customize the appearance of the plot, save it, print it, or zoom in or out. 9 Save Results Table. Data in the Results table can be saved in a tab-, space-, or commadelimited file by specifying the file type and clicking on “Save Results Table.” Thus, users can export these data to other programs for more detailed statistical analysis. Simplified Empirical Models This page allows users to select between three types of simplified empirical models: rigidblock, flexible (coupled), and flexible/rigid (unified). A fourth tab allows users to estimate probability of failure as a function of displacement. Simplified analyses involve no actual integration of strong-motion records but require inputting various parameters into empirically calibrated equations that estimate slope displacement. Rigid. Several types of simplified rigid-block analysis are available. Clicking on any of these analyses (1) causes a description of that analysis to appear in the bottom part of the window and (2) activates data-input boxes that specify what data are required (active boxes turn white). When the required parameters have been entered, click “Compute,” and the estimated Newmark displacement (in centimeters and inches) is shown under “Results.” Flexible (coupled). This tab computes displacement using the empirical model of Bray and Travasarou (2007), which is based on fully coupled, equivalent-linear sliding-block analysis of a modal system. The model requires the following input parameters: Critical acceleration, ac (g), or yield coefficient, ky, which are equivalent. Site period, Ts (s). The fundamental site period can be estimated as 4h/Vs for a 1-D model or 2.6h/Vs for a 2-D analysis of a triangular-shaped sliding mass, where H is the height of the landslide mass and Vs is the shear-wave velocity of the landslide material. Spectral acceleration at 1.5×Ts (g). This can be estimated by calculating the site period (Ts), multiplying by 1.5, and then estimating the spectral acceleration at that period using published attenuation equations such as Abrahamson and Silva (1997, 2008). Earthquake moment magnitude, M. This analysis calculates (1) the probability of zero displacement and (2) an estimate of the non-zero displacement. Results are shown in both centimeters and inches. Flexible/Rigid (unified model). This model was developed by Rathje and Antonakos (2011) to provide reliable results across the full range of flexible and rigid slope conditions. The displacements are based on decoupled, equivalent-linear analysis of layered systems. The model requires the following input parameters: Critical or yield acceleration (g), as used elsewhere. 10 Site period, Ts (s). The fundamental site period can be estimated as 4h/Vs for a 1-D model or 2.6h/Vs for a 2-D analysis of a triangular-shaped sliding mass, where H is the height of the landslide mass and Vs is the shear-wave velocity of the landslide material. Earthquake moment magnitude, M. Peak ground acceleration, PGA (g). Peak ground velocity, PGV (cm/s). Mean shaking period, Tm (s), defined by Rathje and others (2004) as follows: For 5.0 ≤ Mw ≤ 7.25: ln(Tm) = −1.00 + 0.18(Mw − 6) + 0.0038R + 0.078SC + 0.27SD + 0.40(1 − R/20)FD For Mw > 7.25: ln(Tm) = −0.78 + 0.0038R + 0.078SC + 0.27SD + 0.40(1 − R/20)FD where Tm is mean shaking period in seconds, Mw is moment magnitude, R is the closest distance to the fault rupture plane in kilometers, SC and SD are indicator variables that designate site class (SC = SD = 0 for site class B, SC = 1 and SD = 0 for site class C, SC = 0 and SD = 1 for site class D), and FD is an indicator variable that designates forward directivity conditions (FD = 1 for sites with Mw ≥ 6.0, R ≤ 20 km, azimuth angle ≤ 30°, and rupture length ratio ≥ 0.5; FD = 0 otherwise or if conditions are unknown). When the “Compute” button is clicked, several intermediate calculations are displayed under “Calculations”; see Rathje and Antonakos (2011) for a detailed explanation. Under “Results” the estimated displacement is shown in centimeters and inches. Probability of failure. The last tab opens a page that facilitates estimation of the probability of failure as a function of Newmark displacement. Enter the Newmark displacement (cm) in the input box and click “Compute.” The estimated probability of failure (in decimal form) is displayed. This analysis is valid only for fairly shallow, disrupted landslides (shallow falls and slides in rock and debris) and was calibrated using data from the 1994 Northridge earthquake; thus, it is most appropriately applied to those types of slides in southern California. Manage/Add Records The “Manage/Add Records” page allows perusal and graphing of data on all earthquake records in the database and permits the user to add additional records for analysis. The page is divided under two tabs: Manage Records and Add Records. 11 Manage records. The drop-down box at the upper left allows the user to select an earthquake. When an earthquake is selected, all records for that earthquake appear in the data table in the center of the page. Saved groups from the “Group Manager” can also be displayed. Two types of data can be selected for display. If “Display properties of records” is selected, the following seismological properties of the selected records are displayed: digitization interval (s), earthquake (moment) magnitude, Arias intensity (m/s), Duration(5-95%) (s), PGA (g), PGV (cm/s), mean period (s), epicentral distance (km), focal distance (km), rupture distance (km), and focal mechanism. If “Display properties of stations” is selected, the following station properties are displayed: Vs30 (shear-wave velocity of upper 30 m of material at site in m/s), Geomatrix site classification (factor 3), station location (descriptive), station owner, latitude, and longitude. Some data fields are blank for some records if the information was unavailable at the time of publication. Station-owner codes are as follows: • ACOE—U.S. Army Corps of Engineers • BYU—Brigham Young University • CDOT—California Department of Transportation • CDWR—California Department of Water Resources • CGS—California Geological Survey • CWB—Central Weather Bureau of Taiwan • ERD—Earthquake Research Department, Turkey • GSC—Geological Survey of Canada • IRAN—Government of Iran • ITU—Istanbul Technical University, Turkey • JMA—Japan Meteorological Agency • JR—Japan Railway • KOERI—Kandilli Observatory and Earthquake Research Institute, Turkey • LADWP—Los Angeles Department of Water and Power • LAFC—Los Angeles Flood Control • LAMONT—Lamont-Doherty Earth Observatory • MWD—Los Angeles Metropolitan Water District • SCE—Southern California Edison • TPU—Tacoma Public Utilities • UCSB—University of California Santa Barbara • UCSC—University of California Santa Cruz • UCSD—University of California San Diego • USC—University of Southern California • USGS—U.S. Geological Survey • UW—University of Washington • VA—Veterans Administration Geomatrix site classifications (factor 3) are defined as follows: • • A—Rock. Vs > 600 m/s or < 5 m of soil over rock. B—Shallow (stiff) soil. Soil profile up to 20 m thick overlying rock. 12 • • • C—Deep, narrow soil. Soil profile at least 20 m thick overlying rock, in a narrow canyon or valley no more than several kilometers wide. D—Deep, broad soil. Soil profile at least 20 m thick overlying rock, in a broad valley. E—Soft, deep soil. Deep soil profile with average Vs < 150 m/s. Records displayed in the table can be sorted (primarily and secondarily) by any of the listed properties by making selections in the “Sort by” drop-down boxes. Records can be sorted in any combination of ascending or descending order using the drop-down box next to the sort boxes. Records can be deleted from the database by highlighting the record(s) in the data table in the center of the page and clicking “Delete selected record(s) from database.” This permanently deletes the record from the program; a deleted record can only added back by using the “Add Records” procedure below. Information on records can be added or changed using the “Modify record” tab at the bottom of the page. Highlighting a record in the table in the center of the page causes those record properties to appear in the boxes at the bottom of the page. Any of these properties can be modified or, if no data were entered when the records were added, new information can be input. Latitude and longitude must be in decimal degrees. The “Focal mechanism” and “Site classification” boxes have drop-down boxes permitting selection of acceptable choices. When changes have been made in the appropriate boxes, click “Save changes” and the information will be updated. The “Graph record” tab facilitates graphing records in a variety of ways. Begin by highlighting a record in the list. Time series, Fourier amplitude spectrum, and several response spectra can be selected for graphing. If response spectra are to be graphed, the user selects (1) whether the horizontal axis is in terms of frequency or period, (2) the response type, (3) the damping, and (4) the high-frequency cut-off. Clicking “Graph” will generate a separate window displaying the specified graph. Right clicking on the resulting plot box allows the user to customize the appearance of the plot, save it, print it, or zoom in or out. The graphing results can be saved as text values by clicking “Save results as text”; one of three delimiters can be selected. Add Records. Additional strong-motion records can be added to the database and used for analysis. Both individual records and directories containing multiple records can be added. Files must contain only acceleration values in units of g (the acceleration of Earth’s gravity) at a constant time interval (digitization interval); no header data can be in the file. Acceleration values can be delimited in any fashion: spaces, tabs, line feeds, or commas. If files are not in this format, go to the “Utilities” page to convert files to the correct format. Click “Add files/directories to list” to open a browser box to select the file or directory containing the earthquake record(s) to be added. The file or files selected will appear in the import table. The import table contains several columns; some require input, others are optional. The required columns are as follows: Import. Contains a check box to allow selection or deselection of records to be imported. 13 File. Contains the path and file name of each record. This file name is the default record name (see below). This record name can be changed, if desired. Earthquake. Contains the earthquake name. The default earthquake name is the directory name where the files reside, but this can be changed. Earthquake names are unique and form the basis for grouping records throughout the program. To add records for an existing earthquake (including one from the permanent database), input the exact earthquake name in this column, and added records will be added to this earthquake group. To add records for a new earthquake, use a unique name, which must be used for all records for that earthquake. Record. Contains the record name. The default is the file name, but any name can be input. Digitization interval. Contains the digitization interval of the records to be added. Digitization interval is the time spacing (in seconds) between acceleration values in the file. This is a critically important parameter that must be correctly input or the programs will yield incorrect results. Providing data in the remaining columns is optional. However, for added records to be searchable by their various properties, values for those properties must be input. Properties can be input at the time records are added or later through the “Modify record” procedure on the “Manage Records” page. Properties are as follows: Magnitude. Earthquake magnitude. Magnitudes for the permanent records are moment magnitudes. Epicentral Distance. Distance from the recording site to the earthquake epicenter, in kilometers. Focal Distance. Distance from the recording site to the earthquake focus or hypocenter, in kilometers. This can be determined using the Pythagorean Theorem if the epicentral distance and focal depth are known. Rupture Distance. Distance from the recording site to the nearest point on the faultrupture surface, in kilometers. Focal Mechanism. Choices for focal mechanism are listed in drop-down boxes that appear when a box in this column is highlighted. They include strike-slip, normal, reverse, oblique normal, and oblique reverse. Location. Descriptive location of recording site. Owner. Station owner. Latitude. Latitude in decimal degrees. North latitude is positive, south latitude is negative. Longitude. Longitude in decimal degrees. East longitude is positive, west longitude is negative. Vs30. Shear-wave velocity (m/s) of uppermost 30 m of material at the recording site. Site Class. Geomatrix site classification (factor 3), as defined previously. Choices are listed in drop-down boxes and include letter designations A-E. In many cases, entire columns will contain identical data for a given group of records. To fill columns with identical data, use the “Set all values in column” box. Select the column from the drop-down box, and specify the value in the adjacent box. Then click “Set” to fill the columns 14 with the specified value. For “Focal mechanism” and “Site Class,” a drop-down box will be available to select from among acceptable choices. When records have been selected and data entered into appropriate columns, click “Import records” at the bottom left of the page, and the records will be added to the database. Input parameters can be proofed and modified if needed on the “Manage Records” page. After records have been imported, the Import check box is unchecked. If any records cannot be imported due to missing data in required fields or unreadable files, the Import check box remains checked to indicate that the record has not yet been imported. When records are imported, the PGA, PGV, Arias intensity, duration, and mean period are calculated and entered into the database. The file list can be cleared by clicking “Clear list.” Specific records can be removed from the list by highlighting the records and clicking “Clear highlighted records from list.” Utilities This page contains six programs designed to convert existing strong-motion files into different forms. When one of the programs is selected, a brief description of what it does appears in the box at the bottom of the screen, and required input boxes become active. Utility programs can be run on individual files or on all files in a specified directory. For any program selected, the path name for the source file or directory is selected using the browser window adjacent to the “Source file or directory” box. The file and path name for the destination file or directory are specified manually or selected with the browser window adjacent to the “Destination file or directory” box. If a source file contains header information that needs to be deleted, specify the number of lines in the header in the “Delete the first ___ lines of the source file” box. This will create a destination file that contains only acceleration values and no header information, which is the required format for adding a record to the database in “Manage/Add Records.” If a record contains acceleration values in the correct form (units of g) but contains header information that needs to be removed, use the “Multiply by a constant” option, specify a constant value of 1, and specify the number of lines in the header; a new file will be created with the header removed and the data values unchanged. When all of the input boxes have the required data entered, click the “Execute” button to execute the program. The destination file will be written to the location specified. If a file with the name specified in the “Destination file” box already exists, the program prompts the user for permission to overwrite; if the “Overwrite files without prompting” box is checked, the program automatically overwrites the original file without a prompt. The six utilities are as follows: Convert cm/s2 to g’s. This option converts a file containing a sequence of accelerations in units of cm/s2 into a file containing a sequence of accelerations in units of g. The program simply divides each value of cm/s/s by 980.665 to obtain values in terms of g. 15 Convert g’s to cm/s2. This option converts a file containing a sequence of accelerations in units of g into a file containing a sequence of accelerations in units of cm/s2. The program simply multiplies each value by 980.665 to obtain values in cm/s2. Multiply by a Constant. This option multiplies the values in a file by a user-specified constant. The constant is specified in the “Constant” field. This program is useful for files that contain values in units other than g’s or cm/s/s that need to be converted to g’s for use in SLAMMER. Redigitize. This option converts a time file (a file containing paired time and acceleration values) into a file containing a sequence of acceleration values having a constant time spacing (digitization interval) using an interpolation algorithm. The program assumes that the first value in the file is a time value, followed by a corresponding acceleration value, and so on. The digitization interval for the output file must be specified in the “Digitization interval” field; any value can be selected by the user, but values of 0.01-0.05 generally are appropriate. The output (destination) file is in the format necessary to run the other programs in this package, but if the original time file had units other than g, it will be necessary to convert to g before adding the file to the database in “Manage/Add Records.” Bracket records. This option allows users to delete parts of a file that occur before and after a specified value. This is useful in reducing file sizes by eliminating “dead time” in a record. This utility allows the user to retain some points before and after the bracket value for lead-in and lead-out time. Trim records. This option allows users to delete parts of records before and after specific times in the record. In addition to the cut-off times, the digitization interval must be specified. DEFINITION OF TERMS Abbreviations. cm centimeters cm/s centimeters per second cm/s2 centimeters per second squared g acceleration of Earth’s gravity in. inches km kilometers m meters m/s meters per second s seconds Arias intensity. Arias (1970) intensity is a quantitative measure of total shaking intensity that is useful in seismic hazard analysis and correlates well with the distribution of earthquake-induced landslides. Arias intensity is the integral with respect to time (t) of the square of the acceleration, expressed as 16 Ia = π T [a (t )] dt 2g ∫ 2 0 where Ia is Arias intensity (in units of velocity, typically meters per second), g is the acceleration of Earth’s gravity, a(t) is the ground acceleration as a function of time, T is the total duration of strong shaking, and dt is the change in time. An Arias intensity thus can be calculated for each directional component of a strong-motion record. Because Arias intensity is the integral of the entire record, it implicitly accounts for duration, amplitude, and frequency content. Arias intensity is proportional to the RMS acceleration. Coupled analysis. Coupled sliding-block analysis is an extension of decoupled analysis. Coupled analysis models the interaction of sliding/limited shear stresses on the dynamic response of the sliding mass. In SLAMMER, the dynamic response of the sliding mass is computed using a one-dimensional, modal analysis in the time domain (Rathje and Bray, 1999). The sliding mass is defined by its height, shear-wave velocity, and damping ratio; the shear-wave velocity below the sliding mass is also specified (this can be conservatively taken as rock). The modal analysis has a rigid base, but the effects of a visco-elastic base are modeled through additional damping that is assigned based on the Vs of the base and the Vs of the sliding mass (Lee, 2004). The dynamic response can be modeled as linear elastic or equivalent linear. Coupled analysis is considered the most rigorous and yields the most accurate estimates of displacement for deeper landslides in softer material. Critical acceleration. Also known as yield acceleration, critical acceleration is the base acceleration that must be exceeded for a landslide block to begin moving relative to its base. Thus, critical acceleration is the threshold acceleration required to initiate downslope movement. Accelerations below the critical level will cause no permanent downslope movement of the landslide block; once the critical acceleration is exceeded, the landslide will begin to move downslope. The critical acceleration can be determined by iteratively conducting pseudostatic limit-equilibrium analyses until a ground acceleration is found that yields a factor of safety of 1.0, or it can be estimated using the following equation: ac = (FS – 1)g sin α where ac is the critical acceleration in terms of g, the acceleration of Earth’s gravity, FS is the static factor of safety, and α is the thrust angle (the angle from the horizontal that the center of mass of the landslide block first moves). For slope-parallel sliding (infinite slope), the thrust angle is simply the slope angle. Decoupled analysis. Decoupled sliding-block analysis is a modification of traditional Newmark analysis that does not require the potential landslide mass to behave as a rigid block but rather models its dynamic response. Decoupled sliding-block analysis computes the dynamic response of the sliding mass without consideration of sliding and then uses the computed response in a rigid sliding-block analysis. In SLAMMER, the dynamic response of the sliding mass is computed using a one-dimensional, modal analysis in the time domain (Rathje and Bray, 1999). The sliding mass is defined by its height, shear-wave velocity, and damping ratio; the shear-wave 17 velocity (Vs) below the sliding mass is also specified (this can be conservatively taken as rock). The modal analysis has a rigid base, but the effects of a visco-elastic base are modeled through additional damping that is assigned based on the Vs of the base and the Vs of the sliding mass (Lee, 2004). The dynamic response can be modeled as linear elastic or equivalent linear. The most commonly used decoupled analysis was developed by Makdisi and Seed (1978) and estimates the effect of dynamic response on permanent slip in a two-step procedure: (1) Perform a dynamic analysis of the slope (using programs such as QUAD4M or SHAKE) assuming no failure surface; estimate acceleration time histories at several points within the slope and develop an average acceleration time history for the slope mass above the potential failure surface. (2) Use this average time history as the input in a rigid-block analysis and estimate the permanent displacement. This approach is referred to as a decoupled analysis because the computation of the dynamic response and the plastic slip are performed independently. Decoupled analysis thus does not take into account the effects of permanent block movement on ground motion. Digitization interval. Digitization interval is the time spacing between acceleration values in a strong-motion record. Some strong-motion records contain pairs of time and acceleration values, and the time values are not evenly spaced. Such records are called time files; they can be converted to files of acceleration values at a constant digitization interval using the Redigitize program on the “Utilities” page. Duration. Dobry and others (1978) defined a specific measure of the shaking duration of an earthquake acceleration-time history (strong-motion record) based on Arias (1970) intensity. Dobry duration is the time required to build up the central 90 percent of the Arias (1970) intensity; thus Dobry duration is commonly abbreviated as D(5-95%). Dobry and others (1978) proposed an empirical relationship between this measure of duration and earthquake magnitude: log D(5-95%) = 0.432M – 1.83 where D(5-95%) is Dobry duration in seconds, and M is unspecified earthquake magnitude. Dynamic analysis. For flexible sliding masses, decoupled and coupled sliding-block analyses are available (Rathje and Bray 1999). Decoupled sliding-block analysis computes the dynamic response of the sliding mass without consideration of sliding and then uses the computed response in a rigid sliding-block analysis. Coupled sliding-block analysis models the interaction of sliding/limited shear stresses on the dynamic response of the sliding mass. For both decoupled and coupled analyses, the dynamic response of the sliding mass is computed using a one-dimensional, modal analysis in the time domain (Rathje and Bray, 1999). The sliding mass is defined by its height, shear-wave velocity, and damping ratio; the shear-wave velocity below the sliding mass is also specified (this can be conservatively taken as rock). The modal analysis has a rigid base, but the effects of a visco-elastic base are modeled through additional damping that is assigned based on the Vs of the base and the Vs of the sliding mass (Lee, 2004). The dynamic response can be modeled as linear elastic or equivalent linear. 18 Epicentral distance. Epicentral distance is the distance from the earthquake epicenter to the recording site of a strong-motion record. The epicenter is the point on the surface of the Earth directly above the earthquake focus or hypocenter. Equivalent-linear analysis. Equivalent-linear analysis uses strain-compatible soil properties (Vs, damping) in the dynamic analysis of the sliding mass in a manner similar to the site response program SHAKE. The strain-compatible properties are determined through iteration, in which the properties are modified based on the induced shear strain, and then the induced strains are recomputed based on the modified properties. Iterations continue until the modified properties are compatible with the induced strains. The strains used to select the soil properties are computed at mid-depth of the sliding mass. The peak strain is computed at mid-depth and then converted to an effective strain for soil property selection by multiplying by 0.65. Focal distance. Focal distance is the distance from the earthquake focus or hypocenter to the recording site of a strong-motion record. The focus or hypocenter is the point beneath the surface of the Earth where the earthquake rupture initiated. The focal distance is calculated by using the epicentral distance and focal depth in the Pythagorean theorem. Focal mechanism. The focal mechanism of an earthquake refers to the geometry of slip along the fault plane and is classified into the following categories: strike-slip, normal, reverse, oblique normal, and oblique reverse. Fundamental site period. See Site period. kmax. kmax is the maximum value of the k-time history. The k-time history is the seismic loading for the sliding mass and represents the average acceleration within the sliding mass at each time step (Seed and Martin, 1966). kmax also is proportional to the maximum shear force at the base of the sliding mass. Linear elastic analysis. Linear elastic analysis uses the input values of Vs and damping in the dynamic analysis of the sliding mass. Mean shaking period. Mean shaking period, Tm, is a measure of the frequency content of a strong-motion record and is defined as the average period weighted by the Fourier amplitude coefficients over a frequency range of 0.25 to 20 Hz (Rathje and others, 1998; Rathje and others, 2004). Tm was defined by Rathje and others (2004) as follows: For 5.0 ≤ Mw ≤ 7.25: ln(Tm) = −1.00 + 0.18(Mw − 6) + 0.0038R + 0.078SC + 0.27SD + 0.40(1 − R/20)FD For Mw > 7.25: ln(Tm) = −0.78 + 0.0038R + 0.078SC + 0.27SD + 0.40(1 − R/20)FD 19 where Tm is mean shaking period in seconds, Mw is moment magnitude, R is the closest distance to the fault rupture plane in kilometers, SC and SD are indicator variables that designate site class (SC = SD = 0 for site class B, SC = 1 and SD = 0 for site class C, SC = 0 and SD = 1 for site class D), and FD is an indicator variable that designates forward directivity conditions (FD = 1 for sites with Mw ≥ 6.0, R ≤ 20 km, azimuth angle ≤ 30°, and rupture length ratio ≥ 0.5; FD = 0 otherwise or if conditions are unknown). Newmark analysis. Newmark (1965) proposed a method of analyzing the dynamic performance of slopes that effectively bridges the gap between overly simplistic pseudostatic analysis and very sophisticated, but highly complex, finite-element modeling. Although Newmark introduced his method to analyze the performance of artificial embankments, Wilson and Keefer (1983) showed that using Newmark’s method to model the dynamic behavior of landslides on natural slopes yields reasonable and useful results. Newmark analysis is commonly referred to as rigid-block analysis and is explained under the entry for that term. Peak ground acceleration. Peak ground acceleration (MHA, PGA, or amax) is the most widely used measure of earthquake-shaking intensity. It is the maximum absolute value of acceleration in a strong-motion record. Each bi-directional component of a three-component strong-motion record will have its own PGA. Generally PGA is assumed to refer to horizontal ground motions because vertical accelerations are not used in the analyses. Peak ground velocity. Peak ground velocity (PGV) is the maximum absolute value of velocity in a strong-motion record. Each bi-directional component of a three-component strong-motion record will have its own PGV. Generally PGV is assumed to refer to horizontal ground motions because vertical accelerations are not used in the analyses. Period ratio. The period ratio is the ratio of the fundamental site period, Ts, to the mean period of the earthquake shaking, Tm, and is designated Ts/Tm. Reference strain. The reference strain is used to set the nonlinear modulus reduction (G/Gmax, where G is shear modulus and Gmax is the small-strain shear modulus) and damping-ratio curves for the soil within the sliding mass. The reference strain is the shear strain associated with G/Gmax=0.5. The user-specified reference strain is used in the models of Darendeli and Stokoe (2001) for modulus-reduction and damping curves. Rigid-block analysis. Rigid-block analysis, first developed by Newmark (1965), treats a potential landslide block as a rigid mass (no internal deformation) that slides in a perfectly plastic manner on an inclined plane. Thus, the mass experiences no permanent displacement until the base acceleration exceeds the critical (yield) acceleration of the block; when the base acceleration exceeds the critical acceleration, the block begins to move downslope. Displacements are estimated using a two-stage integration procedure: (1) the parts of the acceleration-time history that lie above the critical acceleration are integrated to yield a velocitytime history; (2) the velocity-time history is then integrated to yield the cumulative displacement of the landslide block. Rigid-block analysis yields satisfactory results for relatively thin landslides in stiff or brittle material having period ratios (Ts/Tm) less than about 0.1. For thicker landslides in softer materials, rigid-block analysis tends to be conservative to very conservative. 20 Rupture distance. Rupture distance is the distance from the recording site of a strong-motion record to the closest point on the fault-rupture surface. It can only be determined if a faultrupture surface has been defined seismologically. This distance does not always relate closely to the epicentral or focal distance but is commonly closely correlated with strong shaking and damage. Shear-wave velocity. The shear-wave velocity, Vs, is the velocity with which a shear wave passes through earth material. Shear-wave velocity increases in denser and more competent materials. Thus, softer soils have the lowest shear-wave velocities and harder rocks have the highest shear-wave velocities. Site classification. Site classification refers to the rock or soil conditions beneath a strongmotion station, which can affect the shaking response of the site. We use Geomatrix site classifications (factor 3), defined as follows: A—Rock. Vs > 600 m/s or < 5 m of soil over rock. B—Shallow (stiff) soil. Soil profile up to 20 m thick overlying rock. C—Deep, narrow soil. Soil profile at least 20 m thick overlying rock, in a narrow canyon or valley no more than several kilometers wide. D—Deep, broad soil. Soil profile at least 20 m thick overlying rock, in a broad valley. E—Soft, deep soil. Deep soil profile with average Vs < 150 m/s. Site period. Site period, Ts, is the fundamental period of the potential landslide mass, estimated in a 1-D analysis as 4H/Vs, where H is the maximum vertical thickness of the landslide mass and Vs is the shear-wave velocity of the landslide material. In a 2-D analysis of a triangular crosssection, Ts is estimated as 2.6H/Vs. Spectral acceleration. Spectral acceleration is the motion experienced by a structure, as modeled by a particle on a massless vertical rod having the same natural period of vibration as the structure. It is thus the acceleration experienced at a specific frequency or frequency range. Thrust angle. The thrust angle is the direction the center of gravity of the slide mass moves when displacement first occurs. For a planar slip surface parallel to the slope (an infinite slope), this angle is the slope angle. For simple planar block sliding, the thrust angle is the inclination of the basal shear surface. For circular rotational movement, Newmark (1965) showed that the thrust angle is the angle between the vertical and a line segment connecting the center of gravity of the slide mass and the center of the slip circle. For irregular shear surfaces, the thrust angle can be approximated visually, by estimating an “equivalent” circular surface, or by averaging the inclinations of line segments approximating the surface. Vs30. Vs30 is the average shear-wave velocity of earth material within 30 m of the ground surface. Yield coefficient. The yield coefficient is analogous to critical acceleration; when multiplied by g, it is the acceleration that will initiate downslope movement of a landslide block. 21 REFERENCES CITED Abrahamson, N.A., and Silva, W.J., 1997, Empirical response spectral attenuation relations for shallow crustal earthquakes: Seismological Research Letters, v. 68, p. 94-109. Abrahamson, N.A., and Silva, W.J., 2008, Summary of the Abrahamson and Silva NGA groundmotion relations: Earthquake Spectra, v. 24, p. 67-97. Ambraseys, N.N., and Menu, J.M., 1988, Earthquake-induced ground displacements: Earthquake Engineering and Structural Dynamics, v. 16, p. 985-1006. 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Jibson, R.W., 2007, Regression models for estimating coseismic landslide displacement: Engineering Geology, v. 91, p. 209-218. Jibson, R.W., 2011, Methods for assessing the stability of slopes during earthquakes—A retrospective: Engineering Geology, v. 122, p. 43-50. Jibson, R.W., Harp, E.L., and Michael, J.A., 1998, A method for producing digital probabilistic seismic landslide hazard maps—An example from the Los Angeles, California, area: U.S. Geological Survey Open-File Report 98-113, 17 p., 2 pl. Jibson, R.W., Harp, E.L., and Michael, J.A., 2000, A method for producing digital probabilistic seismic landslide hazard maps: Engineering Geology, v. 58, p. 271-289. Jibson, R.W., and Jibson, M.W., 2003, Java programs for using Newmark’s method and simplified decoupled analysis to model slope performance during earthquakes: U.S. Geological Survey Open-File Report 03-005, version 1.1. 22 Lee, Y.W., 2004, Equivalent-linear dynamic sliding response analysis of geotechnical earth structures: Austin, Texas, University of Texas, Department of Civil, Architectural, and Environmental Engineering, M.S. thesis. Makdisi, F.I., and Seed, H.B., 1978, Simplified procedure for estimating dam and embankment earthquake-induced deformations: ASCE Journal of the Geotechnical Engineering Division, v. 104, p. 849-867. Newmark, N.M., 1965, Effects of earthquakes on dams and embankments: Geotechnique, v. 15, p. 139-159. Rathje, E.M., Abrahamson, N.A., and Bray, J.D., 1998, Simplified frequency content estimates of earthquake ground motions: Journal of Geotechnical Engineering, v. 124, p. 150-159. Rathje, E.M., and Antonakos, George, 2011, A unified model for predicting earthquake-induced sliding displacements of rigid and flexible slopes: Engineering Geology, v. 122, p. 51-60. Rathje, E.M., and Bray, J.D., 1999, An examination of simplified earthquake-induced displacement procedures for earth structures: Canadian Geotechnical Journal, v. 36, p. 72-87. Rathje, E.M., Faraj, Fadi, Russell, Stephanie, and Bray, J.D., 2004, Empirical relationships for frequency content parameters of earthquake ground motions: Earthquake Spectra, v. 20, p. 119-144. Rathje, E.M., and Saygili, Gokhan, 2009, Probabilistic assessment of earthquake-induced sliding displacements of natural slopes: Bulletin of the New Zealand Society of Earthquake Engineering, v. 41, p. 18-27. Saygili, Gokhan, and Rathje, E.M., 2008, Empirical predictive models for earthquake-induced sliding displacements of slopes: Journal of Geotechnical and Geoenvironmental Engineering, v. 134, p. 790-803. 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