Feasibility of Detecting Shallow Events in Dense Array Data With the Source Scanning Method
Date: 4/24/2019
Time: 06:00 PM
Room: Grand Ballroom
Dense seismic arrays provide important opportunities for high resolution detection and location of microearthquakes. Here we examine with synthetic tests the detection/location capability of the source scanning method based on summing square amplitudes (brightness) of predicted arrivals at different stations for various assumed source locations and times. The tests are done in the context of a rectangular array with 100 sensors separated by 100m and S wave arrivals calculated using an assumed S wave velocity model for the shallow crust. We first place a simple explosion source at the array center and 1 km depth and search for the source in model space with 25m horizontal grid intervals, 125m vertical intervals and 0.01s time intervals. We calculate the maximum brightness at each grid point and use the volume with more than 80 percent of peak brightness value as possible location. The vertical and horizontal ranges in the detection volume define the minimum resolvable length (MRL). We separate input signal into multiple frequency bands and apply the detection process to obtain spatial resolution under different frequencies. Then we choose the frequency band with high location resolution and apply the detection process to sources with different epicenters, depths to estimate the spatial dependency of location resolution. The results indicate that the horizontal and vertical MRLs of sources at the array center and 1km depth are larger than 150m and 650m at frequencies below 9Hz and above 15 Hz, respectively. Both horizontal and vertical resolutions decrease with increasing source depth. With increasing epicentral distance, horizontal resolutions decrease but vertical resolutions increase. When the epicentral distance from the array center is larger than 300m, a source located at 1km depth has horizontal MRL > 200m and vertical MRL < 500m. We are currently making corresponding tests using assumed P velocity models and larger aperture arrays. The results of the synthetic tests provide guidelines that will be used to apply the method to recorded dense array data.
Presenting Author: Yifang Cheng
Authors
Yifang Cheng chengyif@usc.edu University of Southern California, Los Angeles, California, United States Presenting Author
Corresponding Author
|
Fangyu Li fangyu.li@uga.edu University of Georgia, Athens, Georgia, United States |
Yehuda Ben-Zion benzion@usc.edu University of Southern California, Los Angeles, California, United States |
Feasibility of Detecting Shallow Events in Dense Array Data With the Source Scanning Method
Category
From Drifting to Anchored: Advances in Improving Absolute Hypocenter Location Accuracy for Natural, Induced and Explosion Seismic Events