Publication Date:
2021-07-03
Description:
Spectral analysis is widely used to estimate and refine earthquake source parameters such as source radius, seismic moment, and stress drop. This study aims to quantify the precision of the single spectra and empirical Green's function spectral ratio approach using the Large‐n Seismic Survey in Oklahoma (LASSO) array. The dense station coverage in an area of local saltwater disposal offers a unique opportunity to observe and quantify radiation pattern effects and subsequent precision of spectral estimates of small earthquakes (M 〈 3). The results suggest that the precision of source properties estimated from direct phase arrivals for arrays with less than 20 stations should be assumed to be not less than 30% and could be as high as 150% if less than five stations are used. Furthermore, we do not see clear evidence for, or against, a scaling of stress drop with magnitude of small earthquakes (M 〈 3) as observed by other studies.
Description:
Plain Language Summary:
Seismologists use ground motion recordings of seismic waves (seismograms) to infer details about the earthquake rupture process. While large earthquakes often generate a physical imprint on the earth's surface through surface rupture, small earthquakes can often only be studied from seismograms. Nevertheless, small earthquakes are of particular interest to learning about the rupture process for many reasons. For example, they are much more numerous than larger magnitude earthquakes and might rupture by the same physical process(es). While seismic arrays are usually restricted to a few to tens of stations, here we use a very large seismic array with 〉1,800 temporary stations to study small earthquakes and how station resolution may bias source property estimates. Source properties include the physical size of the rupture surface and the corresponding slip on that surface, which relate to the amount of stress released by the earthquake. The large number of stations allows us to estimate the source properties in unique detail and test the variability in measurements using different numbers of stations to estimate the precision. We find that the estimation of source properties is highly biased when using a small number of stations (〈20), which should be taken under consideration in future studies.
Description:
Key Points:
We used a Large‐n Seismic Array to investigate the robustness of direct wave spectral estimates.
P wave single spectra reveal azimuthal dependency of corner frequency and long‐ period spectral amplitudes.
P wave single spectra and spectral ratio corner frequency estimates are highly biased by using a small number of stations.
Description:
Deutsche Forschungsgemeinschaft (DFG)
http://dx.doi.org/10.13039/501100001659
Keywords:
551.22
;
550.34
;
earthquake source
;
spectral estimations
;
very large seismic array
Type:
article
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