Non-standard processing modules that are not part of the normal MASW processing procedure, but often necessary and useful, are included under "Utility" in the main menu.
creative in handling those processing results obtained at various stages. The ultimate goal of using the utility modules will be to understand more precisely about data set at different stages of the processing sequence through various approaches of non-conventional non-standard evaluation procedures.
Most modules, except for "Format TEXT data" and "Make Common Seismic Gathers", are accessible within the same "Utility" dialog (Figure 1). The other two modules have their own separate dialogs as illustrated in Figure 2. The type of task each module performs is briefly explained below.
Format SEG-2 Files
The basic and minimum input data element for PS is one record that consists of a suite of an individual channel's recordings, called "traces." The field records should be saved in the SEG-2 format (Pullan, 1990), which is an engineering standard that most engineering seismograph have adopted as the default output format. Other text data files can be converted to the PS format by using a conversion module ("TXT2PS") that can be foud under "Utility" in the main menu. All SEG-2 records are internally converted to PS format as soon as they are imported by the program, and all intermediate and final outputs of seismic data sets will be in this PS format.
All SEG-2 records imported by the ParkSEIS (PS) software are first internally converted to another format called "PS format" that is a modification of the "KGS format (or modified SEG-Y format)" (WinSeis User's Manual, 1997). This conversion is necessary to handle seismic data in a faster and more accurate manner for advanced and non-conventional wavefield operations commonly used in various stages of MASW data processing. In PS format, each channel's data set (called a "trace") is saved as a combina¬tion of a header (of 120 elements of 2-byte integer each), followed by data samples (of 4-byte floating-point value each). A complete listing of the "PS Header" can be displayed by choosing "PS Header" on the main menu's "Info" item. All output of seismic data are saved in PS format with the "DAT" extension (e.g., "Output.dat").
Format TEXT data
Sometimes, seismic data are prepared from a variety of different sources that may include seismographs from different manufacturers, output from numerical modeling, etc. In spite of different data formats adopted in each case, they can be at least prepared in text format. When that is done, these text data samples can be converted to PS format by using this module.
Make Common Seismic Gathers
A normal seismic record in either SEG-2 or PS format has a collection of seismic data that were generated from the same seismic source ("shot"). Therefore, it is also called a "common shot gather." A collection of multiple common shot gathers (i.e., a normal seismic data file in PS format) can be rearranged into different types of "common" gathers based on the primary sorting index. This module can rearrange input seismic data of any type (e.g., common-shot gathers, common-offset gathers, etc.) into the following types of common gathers: offset (CO), receiver station (CRS), source station (CSS), source-receiver mid points (CMP), field record number (CFR), recording channels (CRC), and header word (CHW). In the case of common header word (CHW) gathers, a header word number is specified that is used as the primary sorting index to generate different output records. Usefulness of the common-offset (CO) gathers is further explained in the PS User Guide "Back-Scattering Analysis (BSA) and Common-Offset (CO) Sections."
Make Seismic Walkaway Record
It is sometimes useful to make a seismic record of an extended offset (i.e., source-receiver distance) range simply by combining multiple records obtained at the same surface location but with different source offsets. This "extended offset" record is called a walkaway (or noise analysis) record (Telford et al., 1976; Sheriff, 2002). In seismic data analysis, a walkaway record can be extremely useful in understanding the behavior of seismic body and surface waves in their propagation velocities and attenuation properties. Furthermore, it can produce a dispersion image of an increased resolution achieved by the extended aperture (i.e., offset) of measurement that can delineate multi-modal dispersion patterns more clearly.
Edit Seismic-Data Trace Header
It is sometimes necessary to change one or more of trace header elements to accommodate some experimental modifications or to rectify some minor error introduced during the previous processing (e.g., changing distance unit from feet to meters). This module can accomplish such a task.
Stack (+/-) Seismic Records
This module can stack two different records by summing (+) or subtracting (-) data values. A scaling factor can be applied to each record, if necessary, before the operation. This module can be useful when handling seismic records and dispersion image records (also called "overtone" records) to meet some experimental purposes.
Make 2D Vs Map from Layers
Inversion of one dispersion curve (*.dc) will generate its own output of one layered-earth model (*.LYR). The 2D shear-wave velocity (Vs) cross section is created by combining a multiple number of such LYR files at the end of the inversion that processed a multiple number of input dispersion curves. This module can generate such a 2D Vs cross section from a multiple number of LYR files of your own selection.
One or more layered-earth model (*.LYR) files can be remapped according to a common depth model, which is defined by another "reference" LYR file. This remapping can be useful when comparing files (LYR's) of different depth models, or constructing a 2D Vs cross section from multiple LYR files to bypass some unfavorable interpolation effects introduced by the plotting module.
Figure 1. Utility dialog.
Figure 2.Dialogs for "Format TEXT data" (left) and "Make Common Seismic Gathers" (right) modules.