Regional Seismic Focal Depth Estimation in Complex Tectonic Environments

摘要

The accurate estimation of the depth of small, regionally recorded events continues to be an important and difficult monitoring research problem. In our previous work we developed a combined regional depth estimate, which represents a weighted average of multiple independent measurements of event depths. Our combined measurement includes focal depths found through assisted array processing of early P-wave coda, surface-wave amplitude inversions, and hypocenters estimated from regional travel times. We performed an initial validation of our methodology by applying it to moderate-sized events located within regional distances of the KSAR (Wonju, South Korea) teleseismic array. Our study in Korea showed that the new method produced accurate and consistent depth estimates using regional data. We also found that the IASPEI91 global reference velocity model was appropriate for the relatively simple tectonic region within regional distances of the KSAR array. In this study we further investigate the validity of our regional depth estimator in a more tectonically complex area, specifically in the region around the array in Turkey (Keskin; BRAR/BRTR). The region surrounding the BRAR/BRTR array is dominated by the continental collision between the Eurasian, African and Arabian plates. In a complicated tectonic zone such as this, a global reference velocity model may not adequately predict the regional travel times and amplitudes of observed regional phases, which can potentially lead to poor focal depth estimates. To address this issue we have examined the sensitivity of the depth estimator to the velocity model used in the analyses. We have applied the depth estimator to regional data from well-located events in the Middle East for the IASPEI91 reference and two regional velocity models.