Estimating Faulting Mechanisms From Single-Station Seismic Data
Description:
Earthquakes in sparsely instrumented regions or small earthquakes might be recorded above noise levels at no more than one seismic station. Moreover, small earthquakes do not generate surface waves. Hence it is desirable for the purpose of estimating faulting mechanisms, to use information from body waves recorded at a single station. Polarity and amplitude information for P, SV, and SH waves can more precisely pinpoint the orientation of a shear dislocation faulting mechanism. However, Earth structure that affects body wave amplitudes is often not precisely known and affects theoretical estimates of the amplitudes. To avoid such uncertainties associated with absolute amplitudes, we use relative body wave amplitudes, as well as polarities, to estimate faulting mechanisms. Traditional single-station methods for estimating faulting mechanisms that rely on relative amplitude measurements use amplitude ratios as their data. However, these ratios become unstable when an amplitude in a denominator is small.
Instead, we define the data (body wave amplitude and polarity) as vectors in a 3D space, which continuously represents amplitude combinations for different take-off angles from the focal sphere. Given the take-off angle of the observed amplitudes we perform a grid search over all possible faulting mechanism orientations and select the mechanism that most closely reproduces the observed relative body wave amplitudes. In order to represent the uncertainty in this estimate, we also select a range of mechanisms that produce relative amplitudes and polarities close to the observed ones and assign a weight that is calculated based on noise levels in the seismograms and the geometry of the modeled vectors. In this presentation we demonstrate application of our approach to single-station data from several different types of earthquakes, partially benchmarked against faulting mechanisms derived with established methods. We will demonstrate the method's performance, including optimal conditions for and limitations of the method.
Session: Earthquake Source Parameters: Theory, Observations and Interpretations [Poster]
Type: Poster
Date: 4/18/2023
Presentation Time: 08:00 AM (local time)
Presenting Author: Suzan van der Lee
Student Presenter: No
Invited Presentation:
Authors
Suzan van der Lee Presenting Author Corresponding Author suzan@northwestern.edu Northwestern University |
Madelyn Sita msita@tulane.edu Tulane University |
Victor Agaba victoragaba2025@u.northwestern.edu Northwestern University |
Jochen Braunmiller jbraunmiller@usf.edu University of South Florida |
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Estimating Faulting Mechanisms From Single-Station Seismic Data
Category
Earthquake Source Parameters: Theory, Observations and Interpretations