The ultimate purpose of using ParkSEIS would be to generate either a 1-D (depth) or 2-D (depth and surface) shear-wave velocity (Vs) profile from acquired seismic field records. The entire processing procedure to accomplish that are listed below and illustrated as a flowchart in Figure 1.
1. Field Data (SEG-2 Format)
The original field data set has to be prepared, by first downloading field records from the seismograph. The data set usually consists of a number of multichannel seismic records in SEG 2 format, which is an engineering standard. [One "record" represents a file of seismic data recorded from all channels (e.g., 24-channel). A sub data set from each channel is called a "trace."]
2. Internal Format (PS Format)
SEG-2 data sets are internally converted to the PS (ParkSEIS) format in order to accommodate non-conventional aspects of the MASW data analysis. The output file (if saved from this step) will have a "DAT" extension (e.g., "Output.DAT").
3. Source/Receiver (SR) Setup
This step will encode the field geometry (e.g., receiver spacing, source offset, etc.) and surface coordinates (e.g., survey distance and station numbers) used during the survey into the header of each trace. If a proper encoding has been previously applied by acquisition software during the survey, then the program will provide an opportunity to visually examine the setup in a chart at the beginning of this step. If the original setup is accepted, then the SR setup will be skipped and the process will move to the next step in the process. The output file saved from this step will have a postfix of "(SR)" [e.g., "Output(SR).DAT"]. Refer to PS User Guide "Source-Receiver (SR) Setup" for implementation of this step.
4. Dispersion Image Generation
Each input seismic record (now in PS format) will be transformed to another form of data (also in PS format) whose amplitudes now represent dispersion energy of surface waves so that they can construct dispersion patterns upon display. The output file saved from this step will therefore have as many of such images as number of seismic records in the input file. It will be saved with a postfix of "(*OT)" [e.g., "Output(SR)(ActiveOT).DAT"]. Refer to PS User Guide "Dispersion Image Generation" for implementation.
5. Dispersion Curve (M0) Extraction
One dispersion curve of the fundamental mode (M0) is extracted from each of the input dispersion images previously processed. This M0 curve is saved as a separate file with a "DC" extension and with the record number appended [e.g., "Output(SR)(ActiveOT)(1).DC"]. At the end of this step there can be as many "DC" files saved as number of input dispersion images. Refer to PS User Guides "Dispersion Curve Extraction (1-D Profile)" and "Dispersion Curve Extraction (2-D Cross Section)" for implementation.
Each of input dispersion curve (*.DC) will go through its own process (called "inversion") to find a 1-D (depth) shear-wave velocity (Vs) model whose theoretical M0 curve best matches the input curve. The output will be displayed either in the 1-D Vs profile (if only one "DC" file was imported at the beginning) or in the 2-D Vs cross section (if multiple "DC" files were imported). The 1-D Vs profile of a "layered" velocity (Vs) model will be saved with "(1DVs)" appended and the "LYR" extension [e.g., "Output(SR)(ActiveOT)(1)(1DVs).LYR"], while the 2-D Vs cross section will be saved with "(2DVs)" appended and a "TXT" extension [e.g., "Output(SR)(ActiveOT)(2DVs).TXT"]. Refer to PS User Guides "Inversion (1-D Profile)" and "Inversion (2-D Cross Section)" for implementation.
The flowchart in Figure 1 illustrates how the two special processing modules ["Common-Offset Section" (step 3.1 in the chart) and "Back-Scattering Analysis (BSA)" (step 5.1 in the chart)] can be implemented in association with the overall analysis structure. Refer to PS User Guide "Back- Scattering Analysis (BSA) and Common-Offset (CO) Sections" for implementation of these two steps.
A given processing session may or may not complete all the above steps, depending on the specific purpose of the session. A session may start at an intermediate step, such as at the extraction of dispersion curves (step 5), or a session may process only up to the generation of dispersion images for specific evaluation purposes. The five menus: "Process", "S-Velocity (Vs)", "Dispersion", "Inversion", and "Source/Receiver (SR) Setup" (Figure 2) will provide such flexibilities in the processing sequence.
On the other hand, the "Modeling" menu will provide tools to help either design a survey or clarify specific complications encountered at various stages of data analysis. The "Utility" menu will provide tools to apply nonstandard procedures such as combining seismic records and 1-D velocity (Vs) files. Both "Modeling" and "Utilities" menus will be very useful, especially for experienced users. Refer to PS User Guide "Modeling" and "Utility" for implementation of these two modules.
The "Display" menu will provide visualization of different types of data generated at various stages in the processing sequence. Each display module will also provide additional features for editing and further analysis within the module. Refer to the appropriate PS User Guide for more details about each display module.
The "Settings" menu provides environmental options such as display of the top tool panel and sound options for different types of notifications. The "Info" menu provides information related to this software, and the "Help" menu will show all help files ("User Guide" files) in PDF for this software.
Buttons in each tab of the top tool panel are linked to individual menu items. For example, the first button in the "Display" tab is linked to the first menu item in the "Display" menu (i.e., "Seismic Data") (Figure 3). The main purpose of this "button-driven" execution (rather than "menu-driven") is to expedite the execution of frequently-used operations. A short description of these operations will be displayed as the mouse cursor moves over each button (Figure 4).
Figure 1.Flowchart description of the entire processing sequence to generate shear-wave velocity (Vs) profiles in either 1-D or 2- D format. Two special processing modules for "Common-Offset (CO)" and "Back-Scattering Analysis (BSA)" are also illustrated.
Figure 2.Main menu and the corresponding tool panel displayed above it.
Figure 3.Each button in a tab of the top tool panel is associated with each menu item in the main menu. For example, the first button in the "Display" tab is associated with the first item in the "Display" menu.
Figure 4.Illustration of the hint displayed that describes the type of operation to be executed when the mouse cursor moves over a specific button.