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Using a 1D Radially Symmetric Coda Envelope Model for Robust Moment Magnitude (Mw) Estimation in Iraq’s Tectonically Diverse Zones

Journal Article · · Bulletin of the Seismological Society of America
DOI:https://doi.org/10.1785/0120240113· OSTI ID:2476891
 [1];  [2];  [2];  [3];  [1];  [1]
  1. Univ. of Arkansas, Little Rock, AR (United States)
  2. Patrick Space Force Base, Cocoa Beach, FL (United States). Air Force Technical Applications Center (AFTAC)
  3. Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
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Robust estimation of moment magnitude (Mw) can be challenging for Iraq due to the strong lateral heterogeneity across diverse tectonic zones. We aim to improve moment magnitude estimation by investigating the reliability of using a 1D coda envelope model in diverse tectonic zones of different lateral effects and offer a way forward for reliable estimates of Mw for small events that are difficult to waveform model. Iraq comprises two main tectonic zones: (1) the Outer platform, consisting of the northwestern Zagros fold-thrust belt and the Mesopotamian foredeep, and (2) the Inner Arabian platform which is overlain by the Iraqi desert. A simple 1D coda envelope model was used because coda waves have a low sensitivity to the source and path heterogeneity. Three separate coda calibrations were conducted to investigate the robustness of a single 1D calibration to fit the country: Whole-region calibration, Zagros calibration, and Mesopotamia calibration. In the whole-region calibration, we used stations from both the Zagros and Mesopotamia zones. In the two other calibration models, we used only stations that were in those particular zones. Ground-truth reference spectra derived from the coda spectral ratio method were used to constrain high-frequency site terms. There was no drastic difference when comparing the moment magnitudes calculated from the waveform modeling and the three calibration models. The results show that the 1D coda envelope model is a reliable method even for a region with diverse tectonic zones. Therefore, we recommend using the whole-region calibration model for moment magnitude estimation that provides more complete path coverage and avoids biases introduced by path correction failures. The proposed calibration is a fundamental step in updating the comprehensive earthquake catalog and probabilistic seismic hazard assessments for Iraq.

Research Organization:
Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
Sponsoring Organization:
USDOE National Nuclear Security Administration (NNSA)
Grant/Contract Number:
AC52-07NA27344
OSTI ID:
2476891
Report Number(s):
LLNL--JRNL-865444; 1099533
Journal Information:
Bulletin of the Seismological Society of America, Journal Name: Bulletin of the Seismological Society of America Journal Issue: 3 Vol. 115; ISSN 0037-1106
Publisher:
Seismological Society of AmericaCopyright Statement
Country of Publication:
United States
Language:
English

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58 GEOSCIENCES
Apparent Stress
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Moment Magnitude