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On the Limitations of Spectral Source Parameter Estimation for Minor and Microearthquakes

Description: 

In order to improve the understanding of earthquake source physics and for ground motion modeling in seismic hazard assessment, a reliable estimation of earthquake source parameters is necessary. Due to the increase in the number of stations (including borehole ones), methods traditionally used for investigating the source parameters of earthquakes with M>=3, such as spectral fitting or spectral ratio approaches, are nowadays also extensively applied to smaller magnitude events. However, significant limitations of the usable frequency range spanned by the spectra arise when working with recordings of such minor and micro earthquakes. Low signal-to-noise ratio limits the usage of low frequencies, while the typical sampling rates of seismological networks and the high-frequency attenuation can be limiting factors in the upper end of the usable spectra. In addition, earthquake source parameters determined from ground motion spectra are known to exhibit potentially serious trade-offs, in particular the corner frequency and high-frequency attenuation.

In this study, we investigate the impact of the background wave propagation model on the source parameter trade-offs as well as its effect on the feasibility of obtaining useful source parameters by means of spectral fitting for minor and micro events. The analysis takes advantage of ad-hoc simulated synthetic seismograms with well-defined underlying background propagation where increasing complications in the crustal structure are considered (intrinsic & scattering attenuation). The results show that with given realistic background models and usable frequency bands, the source parameter estimation for minor and micro events can be significantly biased and, not surprisingly, this bias is mainly affecting the estimation of the corner frequency. The results indicate that the source parameters from minor and micro earthquakes should always be viewed with great caution when physically interpreted.

Session: Earthquake Source Parameters: Theory, Observations and Interpretations

Type: Oral

Date: 4/18/2023

Presentation Time: 10:15 AM (local time)

Presenting Author: Stefano Parolai

Student Presenter: No

Invited Presentation: 

Authors