Frequency dependent arrivals of regional P waves from deep earthquakes and their implication for slab structure and configuration
Abstract
The triggering and rupture propagation mechanisms of deep earthquakes remain controversial. The slab structure where deep earthquakes occur is important on understanding the mechanisms. Here we examine frequency dependent arrivals of regional P waves from deep earthquakes, addressing intraslab structure along with configuration of descending slabs. Furumura and Kennett (JGR 2005) showed that P and S waves from deep earthquakes beneath the Sea of Japan have low-frequency onsets followed by high-frequency signals, suggesting the result of small-scale laminar heterogeneity within the subducting Pacific slab. The late arrivals of the high-frequency signals are enhanced for earthquakes deeper than 400 km, probably due to the low-velocity metastable olivine wedge in the slab (Furumura et al., JGR 2016). These results also suggest that high-frequency P-wave delay can be used as a measure to know if the P wave has traveled in a subducting slab. In this study, we present the observations in northern Japan, Fiji, Kermadic, and Ogasawara (Bonin) islands. Delays of high-frequency P waves were observed for Kermadec islands. For Fiji and Kermadic islands, the P-wave onsets appear to be characterized by lower frequencies as source depths are deeper. We found interesting observations associated with the 2015 deeply isolated Ogasawara large earthquake (Mw7.9, depth 664 km, USGS). For an aftershock of the 2015 isolated earthquake, a time difference in P-wave peaks between high and low frequencies was insignificant at a close station to the east. High-frequency P peaks from a deep earthquake in the nearby Wadati-Benioff zone were, however, delayed. The amount of the delay is comparable to those in the Sea of Japan, so the Pacific slab below the Ogasawara islands may have similar intraslab characteristics to that below the Sea of Japan. If the slab extends to the aftershock, its backward bend toward the east above the aftershock can explain the observation. Because high-frequency delays from the aftershock also lacked in western Japan, the slab is likely to be absent in the northwestern side of the aftershock.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.S11A..04K
- Keywords:
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- 3613 Subduction zone processes;
- MINERALOGY AND PETROLOGY;
- 7209 Earthquake dynamics;
- SEISMOLOGY;
- 7215 Earthquake source observations;
- SEISMOLOGY;
- 8170 Subduction zone processes;
- TECTONOPHYSICS