Additional External Researchers:
Won-Young Kim, LDEO
Central United States
A weakness of traditional methods of seismic event location is their susceptibility to errors in picking arrival times of regional phases such as Pn, Pg, and teleseismic phases. We are evaluating the practical utility of waveform cross-correlation as a way to reduce or remove pick error, applied to large datasets in seismically active regions of East Asia, for purposes of obtaining significant improvements in event location.
Key ideas in this proposal have emerged in the last three years from work of a Lamont-led consortium to calibrate stations in East Asia. Thus, we recently found for a number of regions that one of the best methods for obtaining ground truth events was to use waveform cross-correlations that enabled excellent (sub-kilometer) precision in relative locations. Additional (often, non-seismic) information then allowed absolute locations to be estimated. A preliminary study of China has shown that 1300 out of 14,000 earthquakes (approximately 9%) exhibit high cross-correlations with at least one other earthquake, and on this basis we have found 494 sets of cross-correlated multiplets, ranging from doublets to one multiplet with 26 events.
We are applying waveform cross-correlations to the problem of event location in three project areas, namely China, Eastern Canada, and Central North America. For each project area, we have carried out the three steps of data acquisition (digital waveforms, traditional phase picks, catalog information), waveform cross-correlations (exploring the effects of different filters, spatial event separation, and differences in magnitude), and event location (double-difference and absolute relocation).
We regard our main work in this project to be an evaluation of a potentially powerful method – one that can be expected to become increasingly important as the number of digitally well-documented events in a particular region increases, thus increasing the probability that waveform correlation methods can be applied on a large scale.
Cross Cutting Themes:
Hazards and Risk
Air Force Research Laboratory