Date of Award

5-26-2025

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Applied Science

First Advisor

Haydar Al-Shukri

Abstract

The first comprehensive earthquake catalog for Iraq based on moment magnitude (Mw) ‎was compiled by Onur et al. (2017). It spanned the period from 1900 until the end of ‎‎2009, covered the region between 26°–40° N latitudes and 36°–51° E longitudes, and ‎included more than 18,000 earthquakes, of which roughly 4,000 are of Mw 4.0 or larger. ‎With the ongoing efforts of updating the probabilistic seismic hazard assessment ‎‎(PSHA) and the Iraqi building code, the need for an updated earthquake catalog for Iraq ‎in terms of moment magnitude (Mw) has been raised. Robust estimation of moment ‎magnitude (Mw) can be challenging for Iraq due to the strong lateral heterogeneity ‎across diverse tectonic zones. In this study, we aim to improve moment magnitude ‎estimation by investigating the reliability of using a 1-D 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. ‎A simple 1-D 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 are in those particular zones. The results show that ‎the 1-D coda envelope model is a reliable method even for a region with diverse ‎tectonic zones. Several steps were taken to update the earthquake catalog, starting ‎with bulletin compilation. The reviewed earthquake bulletin of the International ‎Seismological Center (ISC) was used as a base, and relocated events were collected ‎and used to enhance the earthquake location. Due to the scarcity of direct Mw ‎estimates, more Mw estimates for earthquake catalog ‎supplementation ‎are important. ‎The catalog was supplemented by directly calculating Mw for about 2800 earthquakes ‎using the coda envelope model of this study (W-Model). The aim was to increase the ‎number of direct moment magnitude measurements in the earthquake catalog. The ‎available Mw measurements were used to develop magnitude conversion relationships ‎for the dominant magnitude types in the catalog (MD, ML, and Mb). The scales were ‎used in cases where the moment magnitude of an earthquake was not directly ‎calculated. The updated earthquake catalog covers the period from 1900 to the end of ‎‎2021 and includes more than 36,000 earthquakes, with approximately 6,200 of them ‎having a moment magnitude of 4.0 or larger. The revised catalog will be utilized to ‎update the PSHA for Iraq. ‎

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