Epicenter relocation of two 2013 earthquake sequences in the Yellow Sea, Korea, using travel-time double-differences and Lg-wave cross-correlation
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We have analyzed two 2013 earthquake sequences from the Yellow Sea of Korea, expecting to provide basic information on offshore seismogenic structures of western Korea. The doubledifference technique with Lg-wave cross-correlation enabled our computation of accurate epicenters for small earthquakes. Including 24 events newly detected by cross-correlation, we relocated 55 events that occurred south of Baekryeong Island after May 17. We employed six stations, including a station 210 km from the epicenters to reduce the azimuthal gap. Relocated epicenters tightly clustered, and led us to deduce a possible rupture plane. We clearly separated two clusters using waveform similarity classification of Lg coda that suggests an east–west strike for the fault-plane solution of the mainshock (M w 4.9). Offshore of the city of Boryeong, more than 150 earthquakes occurred from July through August, which is abnormal seismicity for Korea. We relocate 149 epicenters displaying high waveform similarity using 11 stations with an azimuthal gap exceeding 130°. Relocated epicenters form a 700-m line with clear northeastward progression during the period, and correspond well with the northeast–southwest strike of the fault-plane solution for the largest event (M L 3.8). From the sequence, we classified two spatiotemporally separated clusters by Lg-coda waveform similarity. The clearly observed moveout of Pg arrivals have validated our relocation results.
Key wordsBaekryeong earthquake sequence Boryeong earthquake sequence epicenter relocation double-difference Lg-wave cross-correlation
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