Event couple spectral ratio <i>Q</i> method for earthquake clusters: application to northwest Bohemia
<p>We develop an amplitude spectral ratio method for event couples from clustered earthquakes to estimate seismic wave attenuation (<span class="inline-formula"><i>Q</i><sup>−1</sup></span>) in the source volume. The method allows to study attenuat...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-02-01
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| Series: | Solid Earth |
| Online Access: | https://www.solid-earth.net/10/317/2019/se-10-317-2019.pdf |
| Summary: | <p>We develop an amplitude spectral ratio method for event couples from
clustered earthquakes to estimate seismic wave attenuation (<span class="inline-formula"><i>Q</i><sup>−1</sup></span>) in the
source volume. The method allows to study attenuation within the source
region of earthquake swarms or aftershocks at depth, independent of wave path
and attenuation between source region and surface station. We exploit the
high-frequency slope of phase spectra using multitaper spectral estimates.
The method is tested using simulated full wave-field seismograms affected by
recorded noise and finite source rupture. The synthetic tests verify the
approach and show that solutions are independent of focal mechanisms but
also show that seismic noise may broaden the scatter of results. We apply the
event couple spectral ratio method to northwest Bohemia, Czech Republic, a
region characterized by the persistent occurrence of earthquake swarms in a
confined source region at mid-crustal depth. Our method indicates a strong
anomaly of high attenuation in the source region of the swarm with an
averaged attenuation factor of <span class="inline-formula"><i>Q</i><sub>p</sub><100</span>. The application to S
phases fails due to scattered P-phase energy interfering with S phases.
The <span class="inline-formula"><i>Q</i><sub>p</sub></span> anomaly supports the common hypothesis of highly fractured
and fluid saturated rocks in the source region of the swarms in northwest
Bohemia. However, high temperatures in a small volume around the swarms
cannot be excluded to explain our observations.</p> |
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| ISSN: | 1869-9510 1869-9529 |