Small-scale heterogeneities in the oceanic lithosphere inferred from guided waves
Abstract
We analyze seismic waveforms from deep-focus earthquakes occurring in the subducting slab beneath Japan, recorded by broadband ocean bottom seismometers (BBOBSs) installed on the northwestern Pacific Ocean seafloor. The data reveal waveforms with a low-frequency direct P onset, followed by large-amplitude, high-frequency, long-duration Po and So waves. From the analysis of the BBOBS records and a numerical finite-difference method simulation of seismic wave propagation, we elucidate the generation and propagation processes of such guided waves. We demonstrate that the low-frequency direct P and S waves propagate in the asthenosphere and that the following high-frequency, long-duration Po and So waves are developed by multiple forward scattering of P and S waves. The scattering occurs due to laterally elongated heterogeneities in both the subducting and horizontal parts of the oceanic lithosphere, with the apparent velocities (Vp = 8.1 km/s, Vs = 4.6 km/s) being close to the velocities of oceanic lithosphere.
- Publication:
-
Geophysical Research Letters
- Pub Date:
- May 2013
- DOI:
- 10.1002/grl.50330
- Bibcode:
- 2013GeoRL..40.1708S
- Keywords:
-
- lithosphere;
- oceanic crust;
- computational seismology;
- guided wave;
- oceanic lithosphere