GROUND TRUTH, MAGNITUDE CALIBRATION AND REGIONAL PHASE PROPAGATION AND DETECTION IN THE MIDDLE EAST AND HORN OF AFRICA
In this project, we are exploiting unique and open source seismic data sets 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 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. In the first phase 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 waveform matching. 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. Nine events with magnitudes between 5 and 6 have been studied so far. Source depths for six of the events are within the upper crust, and three are located within the lower crust. The uncertainty in the source depths of the lower crustal events allows for the possibility that some of them may have even nucleated within the upper mantle. Eight events have thrust mechanisms and one has a strike-slip mechanism. We also report estimates of three-dimensional P- and S-wave velocity structure of the upper mantle beneath the Arabian Peninsula obtained from travel time tomography. Travel time measurements were obtained using a data set provided by King Abdulaziz City for Science and Technology (KACST) for the Saudi Arabia National Digital Seismic Network. The network consists of 38 stations (27 broadband and 11 short period). We augmented the KACST data with delay times measured from permanent stations in the region and the 1995-7 Saudi Arabian PASSCAL Experiment. Tomographic images reveal a low velocity feature in the upper mantle stretching north-south beneath the central portion 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:
- 900062
- Report Number(s):
- UCRL-PROC-222767; TRN: US200709%%357
- Resource Relation:
- Conference: Presented at: 28th Seismic Research Review, Orlando, FL, United States, Sep 19 - Sep 21, 2006
- Country of Publication:
- United States
- Language:
- English
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Adjoint Waveform Tomography for Crustal and Upper Mantle Structure the Middle East and Southwest Asia for Improved Waveform Simulations Using Openly Available Broadband Data
Tomographic Imaging of Upper Mantle P- and S-wave Velocity Heterogeneity Beneath the Arabian Peninsula