Ground Truth, Magnitude Calibration and Regional Phase Propagation and Detection in the Middle East and Horn of Africa
In this project, we are exploiting several seismic data sets to improve U.S. operational capabilities to monitor for low yield nuclear tests 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 are being used to perform three related tasks. (1) We are determining moment tensors, moment magnitudes and source depths for regional events in the magnitude 3.0 to 6.0 range. (2) These events are being used to characterize high-frequency (0.5-16 Hz) regional phase attenuation and detection thresholds, especially from events in Iran recorded at stations across the Arabian Peninsula. (3) We are collecting location ground truth at GT5 (local) and GT20 (regional) levels for seismic events with M > 2.5, including source geometry information and source depths. Towards meeting these objectives, seismograms from earthquakes in the Zagros Mountains recorded at regional distances have been inverted for moment tensors, which have then been used to create synthetic seismograms to determine the source depths of the earthquakes via waveform matching. The source depths have been confirmed by modeling teleseismic depth phases recorded on GSN and IMS stations. 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. All of the regional events studied so far nucleated within the upper crust, and most of the events have thrust mechanisms. The source mechanisms for these events are being used to characterize high-frequency (0.5-16 Hz) regional phase attenuation and detection thresholds for broadband seismic stations in the Arabian Peninsula, including IMS stations and stations belonging to the Saudi Arabian National Digital Seismic Network. To improve event locations, source mechanisms and attenuation estimates, new regional P and S wave velocity models of the upper mantle under the Arabian Peninsula have also been developed using data from teleseismic events recorded at stations within the Arabian Peninsula and Horn of Africa. These models show slower-than-average velocities within the lithospheric mantle under the entire Arabian Shield. However, at sublithospheric mantle depths, the low velocity region appears to be localized beneath the western side of the Arabian Shield.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 965952
- Report Number(s):
- UCRL-PROC-232665; TRN: US200921%%542
- Resource Relation:
- Conference: Presented at: 29th Monitoring Research Review, Denver, CO, United States, Sep 25 - Sep 27, 2007
- Country of Publication:
- United States
- Language:
- English
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