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Moment Tensor Uncertainty Analysis for the 2017 Hojedk, Central Iran, Earthquakes Using 1D and 3D Green’s Function

Description: 

Uncertainty analysis is crucial for determining the reliability of a moment tensor solution. Traditional inversion approaches usually provide a single best-fitting solution, ignoring other solutions that may fit the data similarly well. For example, inaccuracies in location and velocity model and signal-to-noise ratio issues can lead to a poor fit between observed and synthetic seismograms such that a wide range of solutions, including those with spurious non-double couple components (ndcc), may fit the data quasi-equally. We use a grid search approach to systematically estimate moment tensor parameter resolution, re-analyzing events from a moment tensor catalog for the Hojedk region in central Iran using the Moment Tensor Uncertainty Quantification (MTUQ) code. The code explores moment tensor solutions through regular grid searches or sampling methods. It also includes statistical analyses to calculate the likelihood distribution of finding the true moment tensor near the best-fitting solution. For a reliable solution, the cumulative likelihood for the assumed correct solution increases rapidly in a short angular distance from the preferred moment tensor. We performed the uncertainty analysis using two velocity models: a 1D model developed for Iran and a regional-scale 3D model for the Middle East. For events above M_w 5.0, we found that the 3D model outperforms the 1D model at long periods (T≥25-30s), requiring smaller time shifts, resulting in lower misfits, reduced spurious ndcc, and yielding more stable solutions. However, for events smaller than M_w 4.0 that require analysis at short periods (T<15 s), where a 3D model would be most beneficial, the 3D model did not outperform the 1D model, with both working well. This is due to the limitations of the current 3D model, which was developed using T≥30s waveforms. Nevertheless, this work represents a step towards implementing more realistic velocity models for waveform modeling in the Middle East. We plan to contribute more in-country data and reliable regional moment tensor solutions to improve the 3D velocity model resolution in the Middle East.

Session: Advances in Reliable Earthquake Source Parameter Estimation - II

Type: Oral

Date: 4/16/2025

Presentation Time: 11:00 AM (local time)

Presenting Author: Felix

Student Presenter: No

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