Ground Truth, Magnitude Calibration, and Regional Phase Propagation and Detection in the Middle East and the Horn of Africa

摘要

In this project, we have exploited unique and open-source seismic datasets to improve seismic monitoring across the Middle East (including the Iranian Plateau, Zagros Mountains, Arabian Peninsula, Turkish Plateau, Gulf of Aqaba, Dead Sea Rift) and the Horn of Africa (including the northern part of the East African Rift, Afar Depression, southern Red Sea, and Gulf of Aden). The data sets have been used to perform two related tasks. (1) We have determined moment tensors, moment magnitudes, and source depths for regional events in the magnitude 4.0 to 6.0 range. (2) These events have been used to characterize high-frequency regional phase attenuation and detection thresholds, especially from events in Iran recorded at stations across the Arabian Peninsula. In the first part of this project, seismograms from earthquakes in the Zagros Mountains recorded at regional distances have been inverted for moment tensors, and source depths for the earthquakes have been determined via matching regional waveforms using a grid search algorithm and forward modeling of teleseismic depth phases. Early studies of the distribution of seismicity in the Zagros region found evidence for earthquakes in the upper mantle. But subsequent relocations of teleseismic earthquakes suggest that source depths are generally much shallower, lying mainly within the upper crust. For all of the events that have been studied, source depths lie within the upper crust. And the events all have thrust mechanisms with E-W or NW-SE striking nodal planes. In the second part of this project, the source mechanisms for these events have been used to characterize high-frequency (0.5-16 Hz) regional phase attenuation and detection thresholds for broadband seismic stations in the Arabian Peninsula, including International Monitoring System (IMS) stations and stations belonging to the Saudi Arabian National Digital Seismic Network.