The 11 March 2011 Tohoku tsunami wavefront mapping across offshore Southern California
The 11 March 2011 (M_w = 9.0) Tohoku tsunami was recorded by a temporary array of seafloor pressure gauges deployed off the coast of Southern California, demonstrating how dense array data can illustrate and empirically validate predictions of linear tsunami wave propagation characteristics. A noise cross-correlation method was used to first correct for the pressure gauge instrument phase response. Phase and group travel times were then measured for the first arrival in the pressure gauge tsunami waveforms filtered in narrow bands around 30 periods between 200 and 3000 s. For each period, phase velocities were estimated across the pressure gauge array based on the phase travel time gradient using eikonal tomography. Clear correlation was observed between the phase velocity and long-wavelength bathymetry variations where fast and slow velocities occurred for deep and shallow water regions, respectively. In particular, velocity gradients are pronounced at the Patton Escarpment and near island plateaus due to the abrupt bathymetry change. In the deep open ocean area, clear phase velocity dispersion is observed. Comparison with numerically calculated tsunami waveforms validates the approach and provides an independent measure of the finite-frequency effect on phase velocities at long periods.
Additional Information© 2015 American Geophysical Union. Received 7 AUG 2014; Accepted 14 APR 2015; Accepted article online 17 APR 2015; Published online 18 MAY 20. The tsunami waveform data from the ALBACORE DPG array are available at IRIS Data Management Center. The IRIS Data Management System is funded through the National Science Foundation and specifically the GEO Directorate through the Instrumentation and Facilities Program of the National Science Foundation under cooperative agreement EAR-1063471. The ETOPO1 and ETOPO2 bathymetry models are made available by the U.S. Department of Commerce, National Oceanic and Atmospheric Administration, and National Geophysical Data Center. We are grateful to Don Forsyth and Spahr Webb for the advice regarding DPG data analysis. We thank John Collins, Steve Ward, and three anonymous reviewers who provided comments that improved this paper. The OBS deployment was made possible with instruments and logistical support of the U.S. National Ocean Bottom Seismic Instrumentation Pool at Scripps Institute of Oceanography; in particular, thanks go to Jeff Babcock, Ernie Aaron, Phil Thai, and Mark Gibaud. The OBS deployment and recovery cruises were made possible with the equipment and logistical support of the University-National Oceanographic Laboratory System vessel fleet and staff support at Scripps with particular thanks to Jon Meyer, Brian Rowe, and Meghan Donohue. Kohler and Weeraratne thank Captain Curl and the crew of R/V Melville for their assistance during the 2010 OBS deployment cruise, and Captain Vullo and the crew of R/V New Horizon during the 2011 OBS recovery cruise. This work was supported by the National Science Foundation (grant OCE-0825254 and CyberSEES-1442665). Lin also acknowledges support for this research from the University of Utah.
Published - jgrb51132.pdf