摘要：We develop an amplitude spectral ratio method for event couples fromclustered earthquakes to estimate seismic wave attenuation (Q−1) in thesource volume. The method allows to study attenuation within the sourceregion of earthquake swarms or aftershocks at depth, independent of wave pathand attenuation between source region and surface station. We exploit thehigh-frequency slope of phase spectra using multitaper spectral estimates.The method is tested using simulated full wave-field seismograms affected byrecorded noise and finite source rupture. The synthetic tests verify theapproach and show that solutions are independent of focal mechanisms butalso show that seismic noise may broaden the scatter of results. We apply theevent couple spectral ratio method to northwest Bohemia, Czech Republic, aregion characterized by the persistent occurrence of earthquake swarms in aconfined source region at mid-crustal depth. Our method indicates a stronganomaly of high attenuation in the source region of the swarm with anaveraged attenuation factor of Qp<100. The application to Sphases fails due to scattered P-phase energy interfering with S phases.The Qp anomaly supports the common hypothesis of highly fracturedand fluid saturated rocks in the source region of the swarms in northwestBohemia. However, high temperatures in a small volume around the swarmscannot be excluded to explain our observations.
