Rigorous Rigid-Block Analysis

This page contains three tabs that sequentially take users through a rigorous rigid-block analysis. The tabs are numbered as sequential steps, including (1) Select Records, (2) Perform Rigid-Block Analysis, and (3) View Results. Each of these steps is explained below:

Step 1: Select Records

This page allows the user to select which earthquake strong-motion records will be used in the analysis. Records can be selected in one of two ways, indicated by the two tabs on this page: (1) search for strong-motion records having specific properties, or (2) search for specific records by earthquake and record name.

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 Help menu 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 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 is displayed. Then click the down arrow under the "Record name" heading. Select the desired record from the list. Then click the "Add record" button 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 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 (e.g., Arias intensity, duration, PGA, source distance, etc.) and properties of the station in general (e.g., location, latitude and longitude, site classification, etc.). 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. The drop-down box to the right of the sort boxes allows any combination of sorting in ascending (A) or descending (D) order. 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 deletes all records from the table; the "Delete highlighted record(s)" button deletes all highlighted records.

Groups of selected records can be saved for future use by using the Group Manager. Click on the "Manage groups..." button to open the Group Manager. 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 import the information displayed in the table into a spreadsheet or other program if other types of analysis on record properties is desired.

When all the desired records have been added to the table and selected, click on the "Go to Perform Rigid-Block Analysis page" button at the bottom right or the "Perform Rigid-Block Analysis" tab on the top of the page to go to the next page.

Step 2: Perform Rigid-Block Analysis

This page allows the user to specify some basic information needed to conduct the Newmark analysis. This information includes specification of (1) the critical (yield) acceleration of the landslide and (2) a scaling value for the strong-motion records.

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. Three choices are available for specifying critical acceleration. If "Constant critical acceleration" is selected, a single value (in g's) 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. If "Varies with time" is selected, the user can enter pairs of time/critical acceleration values to define a curve of varying critical acceleration as a function of time in the same manner as described above. Again, each successive time value must be greater than the previous value.

Under "Scaling", two options are available. The first option, "Do not scale earthquake records", analyzes each record using the original, unaltered acceleration values. The second option, "Scale all earthquake records to a uniform PGA", compares the specified peak ground acceleration (PGA) to the PGA of each record, calculates a scaling factor for each record, and scales all acceleration values in that record accordingly. Thus, all selected records are scaled to a common PGA specified by the user. If this option is selected, simply enter the desired PGA (in g's) in the data field.

When all parameters have been entered on this page, click the "Perform Analysis" button at the lower left, or click the "View Results" tab on the top of the page and then click the "Perform Analysis" button on that page. The processing time depends on the number of records selected, and processing large numbers of records on slower computers might require long processing times. A progress indicator should appear to show the progress as each record is analyzed.

Step 3: View Results

After the "Perform Analysis" button has been clicked, the selected records will be analyzed, and the results will be displayed in a table. The table shows the earthquake name, the record name, and Newmark displacements. Two Newmark displacements are shown for each record analyzed: one for the "top" or positive accelerations, and one for the "bottom" or negative accelerations. The average of these two displacements is displayed in the far right column. All displacements are given in centimeters. At the bottom-right of the table, the mean, median, and standard deviation of the average displacements are shown (standard deviations are calculated using the sample, or unbiased, model). Data in the table can be saved in tab-, space-, or comma-delimited file by clicking on the "Save output" button. Thus, users can export these data to other programs for more detailed statistical analysis.

A histogram of the Newmark displacements can be displayed by clicking the "Plot histogram of Newmark displacements" button. 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 number of bins in the histogram can be specified in the box to the right of the button; the default is 10.

A plot showing a time history of Newmark displacements can be generated by clicking on the "Plot Newmark displacements versus time" button. 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 legend" box will display a legend keying colors of curves to specific earthquake records. There are a limited number of colors available for plotting, so plots having large numbers of records will have duplicate colors for some records. Plotting displacements for large numbers of records can take several seconds or tens of seconds; during this time the plot window will display a plain gray background until the plot appears.

Click on the "Clear output" button in the upper left part of the page to clear the currently displayed results and any corresponding plots.