Upper Mantle Q Structure Beneath Old Seafloor in Western Pacific
Abstract
The PLATE (Pacific Lithosphere Asthenosphere Thickness Experiment) ocean bottom seismometer array south of the Shatsky Rise provides an opportunity to image the attenuation structure of the upper mantle in one of the oldest parts of the Pacific Ocean. The array, deployed from October 2009 to November 2010, provided data from eight seismometers that spanned a lateral extent of 200 km by 600 km. Intermediate and deep focus earthquakes in the Mariana and Izu Bonin subduction zones provide paths that probe different depths within the mantle beneath the westernmost Pacific. Event depths range from 150 km to 450 km. Data from nearby island arc stations, GUMO and SAIP, were also included in the analysis. After correcting for instrument response, displacement amplitude spectra from the P-wave vertical component were calculated for 1 s, 2 s and 4 s windows starting at the P arrival time. Spectra were inverted for t* and corner frequency values, assuming that each event shares a common corner frequency for all stations; t* estimates were converted to estimates of path-averaged Q. Pn propagation indicates very high Q values in the lithosphere, on the order of several thousand or more. This result, coupled with path-averaged Q values, indicates that average Q values in the sub-lithospheric upper mantle are on the order of 400. Given the range of source depths and epicentral distances represented in the study, further analysis should enable us to deduce the vertical Q structure of the upper mantle beneath this region of old oceanic lithosphere.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.T51C2601B
- Keywords:
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- 7203 SEISMOLOGY / Body waves;
- 7208 SEISMOLOGY / Mantle