Home Articles An Interactive Programme for Deterministic Seismic Hazard Assessment

An Interactive Programme for Deterministic Seismic Hazard Assessment

Suman Jain
3074 IIT Kanpur
India
Email: [email protected]

Using the technique of GIS (geographic information systems), C++ and (arc) macro language programming is a user-friendly programme used for spatial data input, processing, manipulation, analysis, modelling and presentation for deterministic seismic hazard assessment. Analytical and technical capabilities of the technique of GIS is used to organise spatial (geographic, such as X, Y coordinates) and aspatial (attribute) data, and to understand their spatial relationships, providing a basis for seismic hazard study, hazard prediction, risk assessment and hazard management. C++ and arc macro language (AML) programming automates the input command sequence for different Arc/Info (ESRI, 1999) based GIS software command sequence and other frequently performed actions. The data are stored in a relational database structure (RDBMS) such that it is easy for the user to extend this programme and to allow full use of the relational database methods. This information will be used for seismic (Panza et. al. 1999) zonation and microzonation, to make realistic prediction of the ground motion, pre-event localized planning for disaster mitigation and civil protection.

Design Philosophy:
Past approaches taken for spatial data input, processing, analysis and presentation used for the deterministic seismic hazard assessment study were time consuming, costly and limited one’s ability to perform analysis. Researchers and potential users are not too familiar with (Arc/Info) GIS based software. Moreover, no software package satisfies every need that will eventually arise in solving a real world problem. An analyst often needs direct access to spatial data and other attributes to process the information and some other programme or software may be appropriate for some purposes. An interactive programme is designed to serve the needs of seismic hazard scientists, be inexpensive, be timesaving, and be easy to use and extend. By fulfilling these needs, it is hoped that this programme will facilitate an easy-to-use graphical interface, low cost, time, and end-user extensibility. Arc/Info GIS based software was customised for study purposes and this end-user GIS based software application includes a number of programmes written in C++ and AML for input, output and data manipulation. The data storage is designed and developed such that the user can access database also with other programmes.

Programme Description:

Jabalpur Earthquake

This is a user-friendly programme that runs on SUN Workstations (and compatible operating systems) and Arc/Info GIS based software (version 7.2.2). However, with minor changes, it can be implemented on PCs. This methodology is designed for people with little or no experience using Arc/Info GIS based software. However, it is assumed that one has some basic knowledge of the computer operating system and GIS. This programme uses graphical interface providing standard interface elements, such as menus and selection of items from lists, and guides the analyst through spatial data input, reformats it to Arc/Info specific format, attaches attribute specific data to it, performs spatial analysis operations (such as overlay) for feature / data manipulation and prepares the data for further analysis, to be used in decision making and presentation. The choice(s) or selection of items from the list are easy to follow and prompts input from the user, such as input/output filename or attribute name etc. This is a complete stand-alone programme. Arc macros help to automate the sophisticated spatial operations that otherwise would have required specific Arc/Info GIS based software command input. Although designed and developed especially for deterministic seismic hazard assessment, this methodology can be easily modified to solve many real world problems and functions for which the technique of GIS is used.

Programme Operation and Example(s):
This programme is designed to allow the user to perform different tasks to obtain the desired end results. Before operating this programme, certain points have to be considered. The most important point in building a database is automating the data, i.e., convert the spatial data to digital format. And to make this spatial data usable, it is important that it is free of errors and spatial data defines the spatial relationship between spatial or geographic (point, line and area) features (ESRI, 1999). Arc/Info GIS based software requires specific format for the input data. The data from real-world coordinates, however, is available in varying formats. To overcome this, programming constructs of the C++ language are used to reformat spatial data to Arc/Info GIS based software format. These C++ programmes can be compiled and run at the operating system prompt (a C++ compiler is required). The reformatted data can then be input into Arc/Info GIS based software to generate coverage(s) or data layers. The input data used for this hazard study includes Ground Shaking Data or GSD (to include Displacement, Velocity, Acceleration and DGA or Design Ground Acceleration data), Intensity Data (max. macroseismic intensity for the entire study area and max. intensity felt in every municipal land), Polygon Data (representing seismogenic zones).

Jabalpur Earthquake

The programme session starts operating at the Arc/Info GIS based software (systems) prompt ‘arc’ and by running the main programme file. The user is given the following choices from the main menu:

  1. Getting Spatial Data into Arc/Info
  2. Spatial Operations for Feature Manipulations
  3. Spatial / Statistical Analysis.
  4. Output (graphical, report, maps etc.)
  5. To Quit This Program

There are sub-choices within the main choices and further choices within these sub-choices that are easy to follow. For example, if the user selects ‘A’, then the following sub-choices are presented:

  1. GSD Data
  2. Intensity Data
  3. Polygon Data
  4. Generate Grid
  5. Go to Main Menu
  6. Quit

Upon selecting sub-choice ‘A’, for example, two sub-choices are given:

  1. To Display Coverage
  2. Create a Coverage

This sub-routine (A) allows the user to display, interpret and query the contents of a coverage or thematic map. The user can retrieve information on spatial features by double clicking with the mouse. Note that coverage or thematic map is a set of spatial features retrieved from a table or view in the database. The coverage(s) can be created interactively (sub-routine: B), saved to the disk and can be loaded in later sessions (sub-routine: A). For example to create a point coverage showing displacement peak values, the user selects ‘B’ and is given the following prompt:

‘ENTER INPUT X, Y COORD FILENAME’ itasmf0res.amx

‘ENTER INPUT .DAT FILENAME’ (To attach attribute information) itasmf0res.dat

‘ENTER OUTPUT COVERAGE NAME’ C:/mydir/Displmnt

The output is coverage named Displmnt in the user’s workspace. Note how this programme requires minimum input from the user in the form of input, output filename(s) only. Thus, by reformatting data using C++ routines and main menu choice A and its given sub-choices, different data layer(s) can be created. Each layer contains specific information related to the deterministic seismic hazard assessment study. However, to identify new associations between the data layers, it is necessary to further manipulate this data and apply spatial analysis operations Continued from page 39 (such as overlay) that produces meaningful results (choice B of main menu facilitate this). The next step is to prepare and manipulate the derived data for statistical / spatial analysis. Since the study objective is to use deterministic modelling to derive reliable, region specific, correlation relations (between the maximum felt macroseismic intensity and displacement, velocity and DGA etc.), to make realistic prediction of seismic parameters (such as ground motion), seismic microzonation etc., a number of AMLs were written to this end with the following choice(s)

Statistical/Spatial Analysis

  1. Preparation of Input File
    1. Select Input file for Tabular Analysis
    2. Take Log10 Attach Log Values
    3. Generate Average/Menu Values
    4. Take Log10 of Mean Values
    5. Prepare Sample file for Regression Analysis
  2. Run regression Analysis

Through these sub-routines, the user can select the coverage or file and the attribute parameter(s) for statistical (regression) analysis, go through different tasks if desired (there are further routines to perform these and the user input is in the form of file or attribute name(s).

Summary
This programme is designed and developed with the goal of automating and implementing the problem solving operand for deterministic seismic hazard assessment. Tasks not included in this programme, such as graphs, reports and annotating maps for presenting the results of the analysis, can be easily performed and arc macros can be written to this end. Experimental sessions at ICTP indicate that it is user-friendly, easy to use and saves time and cost. At present, this programme is applicable by the students and practising seismic scientists for micro level.

Acknowledgement:
This programme was developed during a UNESCO funded scientific visit to ICTP, Italy. I thank Prof. G. F. Panza, head of the SAND (Structure and Non-Linear Dynamics of Earth) research group for support, Drs. Franco Vaccari and AbdelKarm Aoudia data and suggestions throughout this work.