An analysis of ground shaking and transmission loss from infrasound generated by the 2011 Tohoku earthquake

Citation:
Walker, KT, Le Pichon A, Kim TS, de Groot-Hedlin C, Che IY, Garces M.  2013.  An analysis of ground shaking and transmission loss from infrasound generated by the 2011 Tohoku earthquake. Journal of Geophysical Research-Atmospheres. 118:12831-12851.

Date Published:

2013/12

Keywords:

alaskan earthquake, atmosphere, earthquake infrasound, Gravity waves, ground shaking, infrasound attenuation, infrasound transmission loss, location, propagation, ShakeMaps, surface explosions, velocity, waves

Abstract:

The 2011 M(w)9.0 Tohoku earthquake generated infrasound that was recorded by nine infrasonic arrays. Most arrays recorded a back azimuth variation with time due to the expanse of the source region. We use ray tracing to predict group velocities and back azimuth wind corrections. A Japan accelerometer network recorded ground shaking in unprecedented spatial resolution. We back projected infrasound from arrays IS44 (Kamchatka) and IS30 (Tokyo) to the source region and compare these results with acceleration data. IS44 illuminates the complex geometry of land areas that experienced shaking. IS30 illuminates two volcanoes and a flat area around the city of Sendai, where the maximum accelerations occurred. The arrays and epicentral region define three source-receiver profiles. The observed broadband energy transmission loss (TL) follows an exponential decay law. The best fitting model, which has parameters that are interpreted to include the effects of geometric spreading, scattering, and the maximum ratio of the effective sound speed in the stratosphere to that at the ground (accounts for stratospheric wind speed), yields a 65% variance reduction relative to predictions from a traditional TL relationship. This model is a simplified version of the model of Le Pichon et al. (2012), which yields an 83% variance reduction for a single frequency, implying that fine-scale atmospheric structure is required to explain the TL for stratospheric upwind propagation. Our results show that infrasonic arrays are sensitive to ground acceleration in the source region of megathrust earthquakes. The TL results may improve infrasonic amplitude scaling laws for explosive yield.

Notes:

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Website

DOI:

10.1002/2013jd020187