← Back to Gallery

Uncertainty Estimates for Moment Tensors and Quantities Derived From Them From Comparison of Global Catalogs

Analysis of moment tensor catalogs gives insight into general properties of many earthquakes beyond what can be obtained by studies of individual earthquakes and allows estimating uncertainties in the determination of seismic source processes. Traditionally, uncertainties in moment tensors are derived from the misfit between observed and synthetic waveforms. However, the differences between moment tensors in the USGS and the Global CMT Project catalogs are typically an order of magnitude larger than the reported errors, suggesting that the reported errors substantially underestimate the uncertainty due to different inversion procedures. Differences between double-couple (DC) components decrease with magnitude, and correlation between non-double-couple (NDC) components increases, suggesting that seismic sources of large earthquakes are determined more reliably. A dataset compiled from three global and four regional catalogs shows that NDC components are essentially independent of magnitude for earthquakes over a large magnitude range, with a mean deviation from a DC source of about 20%. Additionally, there is essentially no difference in NDC components between earthquakes with different fault mechanisms and in different geologic environments. This consistency indicates that most NDC components, especially for smaller earthquakes, do not reflect real source processes and are likely to be artifacts, presumably due to not accounting for laterally varying Earth structure during the inversion. Numerical experiments confirm this result. Generating synthetic seismograms for a perturbed Earth model and inverting them using the unperturbed Earth model yields NDC components whose size is similar to the ones reported in global moment tensor catalogs. Comparison of NDC components in three global catalogs allows quantifying the noise contained in them and shows that the GCMT catalog provides the most precise NDC components. Furthermore, this comparison reveals that NDC components of large earthquakes are more reliably determined and that the largest NDC components are more likely to represent real source processes.

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

Type: Oral

Room: Tubughnenq’ 3

Date: 5/3/2024

Presentation Time: 02:30 PM (local time)

Presenting Author: Boris Rösler

Student Presenter: No

Additional Authors