SurfSeis Version 2.0 Overview

Since the release of SurfSeis version 1.0 in 2000, the surface wave method in general has gone through a tremendous amount of applications and research at many places, including the Kansas Geological Survey (KGS). In consequence, SurfSeis 2 has new features that take into account those new methodological developments as well as users' demands for enhanced user-friendliness. Although the manual (Manual20.pdf) has been prepared mainly to explain the new features, such as those related to the passive part of the multichannel analysis of surface waves (MASW) method, it can serve as a stand-alone manual for both active and passive MASW methods for those who have previous experience in seismic data acquisition and data processing in either body- or surface-wave methods.

In this version, the MASW method has been divided into three categories by survey mode: active, passive remote, and passive roadside MASW methods (Figure 1). The active method (Park et al., 1999) was introduced in previous versions of SurfSeis. It is the conventional mode of survey using an active seismic source (e.g., a sledge hammer) and a linear receiver array, collecting data in a roll-along mode. You can also use a fixed spread, if you have more geophones, to emulate roll-along acquisition with fewer phones. The other two methods utilize surface waves generated passively from ambient cultural (and natural) activities such as traffic (and thunder, tidal motion, atmospheric pressure change, etc.). The passive remote method (Park et al., 2004; 2005) employs a two-dimensional (2-D) receiver array such as a cross or circular layout to record passive surface waves. This results in the most accurate evaluation of shear-wave velocity (Vs) at the expense of more intensive field operations and the burden of securing a wide open space for the array. This can be a good choice if a relatively regional one-dimensional (1-D) Vs profiling is needed. The passive roadside MASW method (Park and Miller, 2006) adopts the conventional linear receiver array and tries mainly to utilize those surface waves generated from local traffic. It tries to overcome limitations with the passive remote method such as difficulty in securing a spacious area and inconvenience in field operations by sacrificing the accuracy (usually less than 10%) of the Vs evaluation. With this method, the array can be set along the sidewalk or the shoulder of a road and the survey can continue in a roll-along mode for the purpose of 2-D Vs profiling. Using a land streamer for the array can improve the survey speed by as much as a few orders of magnitude. In addition, an active impact (e.g., by using a sledge hammer) can be applied at one end of the array to trigger a long (e.g., 30 sec) record of data. This can result in the active-passive combined analysis of surface waves for the purpose of obtaining both shallow (e.g., 1-20 m) and deep (e.g., 20-100 m) Vs information simultaneously. A more detailed description of each method can be found in previously cited references. However, field procedures for these methods (both passive and active) have been summarized in this version of manual. Data processing steps are explained by using the sample data sets stored in the "...\SurfSeis20\SampleData\" folder. All acquisition parameters for the sample data sets are listed in Table 1.

Figure 1a--Active MASW method. More information is available on "Active MASW."

Figure 1b--Passive Remote MASW method. More information is available on "Passive Remote MASW."

Figure 1c--Passive Roadside MASW method. More information is available on "Passive Roadside MASW."

Table 1--Summary of sample data set parameters.

A summary of the entire procedure with a MASW method (active or passive) is displayed in the flowchart in Figure 2. Major changes and new features with this version are summarized as follows:

1. Modules to process passive surface waves have been added in addition to the previously existing active module (Figure 1). Two different types of passive surveys are available: one, called the passive remote MASW method, uses a two-dimensional (2-D) receiver array and the other, called the passive roadside MASW method, uses the conventional 1-D linear array.
2. The way dispersion analysis is executed has been changed so that the previous sequence of 'Preprocess-->Overtone-->Run-->Save' has been divided into two separate steps: (1) generation of dispersion image (called overtone, OT) data and (2) mouse-aided extraction of the dispersion curve from the image. The previous sequence, however, can still be accessed by right-clicking (instead of normal clicking) the 'Dispersion' button in the analysis menu when importing an input seismic file.
3. A new mode of inversion has been added. This is a general Monte-Carlo method applied directly to the dispersion image (instead of the dispersion curve), seeking the best-matching solution through a random search. With this process, up to four modes of dispersion can be accounted for and all the parameters in a 5-layer earth model can be manually changed, if desired, to compare theoretical curve(s) with dispersion trend(s) in the background image.

Most (if not all) of the bugs existing in previous versions of SurfSeis have been fixed, thanks to the comments and reports from many practitioners who used SurfSeis to conduct the MASW method and who were very patient and always willing to help this quite new geophysical method still in its infancy evolve into a better form. We researchers at KGS sincerely appreciate your patience and assistance.

Figure 2--Flow chart of MASW processing steps.

References

Park, C.B., and Miller, R.D., 2006, Roadside passive MASW: Proceedings of SAGEEP, April 2-6, 2006, Seattle, Washington. [PDF available online, 1.3 MB]

Park, C.B., Miller, R.D., Ryden, N., Xia, J., and Ivanov, J., 2005, Combined use of active and passive surface waves: Journal of Engineering and Environmental Geophysics (JEEG), 10, (3), 323-334. [PDF available online, 1.1 MB]

Park, C.B., Miller, R.D., Xia, J., and Ivanov, J., 2004, Imaging dispersion curves of passive surface waves: SEG Expanded Abstracts: Soc. Explor. Geophys., (NSG 1.6), Proceedings published on CD. [PDF available online, 736 kB]

Park, C.B., Miller, R.D., and Xia, J., 1999, Multichannel analysis of surface waves (MASW); Geophysics, 64, 800-808. [PDF available online, 1.3 MB]

SurfSeis 2.0 Processing Steps

Field Setup (Active Survey)

Active Data Set Acquired in Roll-Along Mode

Encoding Field Geometry

Source-receiver Station Table after Encoding

Field Setup (Passive Remote Survey)

X-Y Coordinate Setup for Each Receiver by Click and Drag

24-Channel Circular Array (After Completion of Setup)

48-Channel Cross Array (Early Stage of Setup)

Field Setup (Passive Roadside Survey)

Passive Roadside Data Set Acquired in Roll-Along Mode

Encoding Field Geometry

Source-receiver Station Table after Encoding

Dispersion Image Generation

Generation by 2-D Wavefield Transformation

Controllable Processing Parameters

Active (A) and Passive (P)

Passive (P) Only

Active (A) and Passive (P)

Active (A) and Passive (P)

Dispersion Image

From Active Data

From Passive Remote Data

Azimuth Information of Passive Remote Data

Dispersion Curve Extraction

Setting Bounds by Mouse for Phase Velocity and Frequency Ranges

Extracting and Editing Dispersion Curve

Controllable Parameters

Inversion of Extracted Curves

Gradient-Based Inversion* of (Fundamental Mode) Dispersion Curves

*If all extracted curves are of the fundamental mode, this is the fastest and simplest inversion approach to take.

2-D Vs Profile from Inversion

Inversion of Dispersion Image

Multi-modal (up to 4) Forward Modeling with Full Control of Earth Model*

*If multi-modal nature is observed with dispersion image, this provides a complete control over dispersion trends modeled from a given earth model to be compared to background images.

Automatic Inversion by Monte-Carlo Approach for 2-D Vs Profile

Multi-Modal Inversion (Controls)

Forward Modeling Portion

Inversion Portion

Combining Active and Passive Dispersion

To Increase Frequency (Depth) Range...

To Help Modal Identification...

Opening an Active (or Passive) Image and then Passive (or Active) Image to Combine Together

How to Use a Fixed Spread with SurfSeis Software to Emulate a Roll-along Data-acquisition Pattern

If you have estimated the necessary number of seismic spread channels (say, 24) and you have the ability to acquire data using a larger number of channels (say, 48), then you may find it more labor efficient to acquire MASW data using a fixed spread. Seismic records can be obtained by shooting from one end of the spread and then continuing shooting into the spread (moving the source toward the middle of the spread). Then, from the data acquired in such a manner data, record traces can then be extracted (cut) to emulate a roll-along data acquisition pattern with a smaller spread (e.g., having 24 channels).

An example:

Assume the 48 geophones are located on stations 1001-1048 and a total of 13 seismic records were shot (acquired) with the source located at stations 999, 1001, . . . . through 1023 for the records numbered from 101 to 113. SurfSeis can help you pull out (extract, cut) thirteen 24-channel records using the following steps.

1. Convert data from seg2 to kgs format (say, line1.dat).
2. Apply geometry information (Field Setup) into the trace headers.
3. Click 'Display,' then 'Seismic' buttons, and open the converted kgs data file (say, line1.dat).
4. 4. Find the "scissors" button located at the top right corner of the window displaying seismic data. (The "scissors" button is located on the row containing the pointing-hand buttons. If you do not see these buttons, click the 'Record. . .' label to activate/deactivate that row of buttons). Click the "scissors" button to display a 'Cut Records' window containing three tabs ('Record,' 'Trace,' and 'Time').
5. At the 'Record' tab select the end record at the 'End' drop box, or check the 'All Records' checkbox.
6. Click 'Save Output As' button to specify the output file name (the default in this example would be line1(CUT).dat.)
7. At the 'Trace' tab select the 'Begin' and 'End' trace numbers (e.g., 1 and 24). At both Increment boxes select 2 (this is because your source moved with 2 geophone intervals, i.e., 999, 1001, etc.)
8. Click the 'OK' button to extract (cut) the new set of records each containing now only 24 traces.
9. Open the new file (e.g., line1(CUT).dat) and go through the records using the pointing-hand buttons to make sure you have extracted the intended range of traces from each record.