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Using a 1-D Radially Symmetric Coda Envelope Model for Robust Source Scaling in Iraq's Tectonically Diverse Zones

Description: 

Estimation of moment magnitude can be challenging for Iraq due to the strong lateral heterogeneity of the diverse tectonic zones. In this study, we investigate the reliability of using 1D coda envelope model for the entire country despite the lateral effects and the differences in the tectonic zones' geophysical characteristics. Iraq comprises two main tectonic zones: 1-The Outer Platform which consist of the northwestern Zagros Fold-Thrust Belt and the Mesopotamian Foredeep; 2-The Inner Platform that is covering the Iraqi western desert. Due to the fact that coda waves have a low sensitivity to the source and the path heterogeneity, a simple 1-D coda envelope model was used. Three separate coda calibrations were conducted in order to investigate the reliability of using one calibration for the country, Iraq calibration, Zagros calibration, and Mesopotamia calibration. 51 events (Mw>4.5) recorded by ten stations were used for Iraq calibration while for Zagros calibration, 42 events from three stations located within Zagros zone were used. The last calibration is for Mesopotamian Foredeep, where there are 7 stations in this zone. 40 events with Mw>5 were enough to calibrate the zone. Ground truth (GT) reference spectra derived from the coda spectral ratio method were used to constrain high-frequency site terms. There were no drastic differences when comparing the moment magnitudes that were calculated from the three calibrations. However, Zagros calibration showed a better estimation of the apparent stress because the apparent stress that we used as references for the calibrations were located in Zagros zone. We could not find good candidate events in Mesopotamia to calculate the apparent stress due to the low seismicity. As a result of this study, we recommend using Iraq calibration since 10 stations were used in this calibration giving it the best path correction, and there were slight differences in the estimated magnitudes of the three calibrations. The proposed calibration serves as a fundamental step to update the comprehensive earthquake catalog for Iraq and probabilistic seismic hazard assessments.

Session: Understanding and Quantifying the Variability in Earthquake Source Parameter Measurements - I

Type: Oral

Date: 5/3/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Muntadher

Student Presenter: Yes

Invited Presentation: 

Authors