Fred Schwab

Typhoon-generated microseisms observed from the short-period KSRS array

The seismic-noise data recorded on 19 vertical-component short-period seismometers of the KSRS seismic array are analyzed (1) to determine whether typhoons in the Pacific Ocean can be tracked accurately, and (2) to explore the seismic phases comprising the noise field recorded at the array. For our tests, two super typhoons, Sinlaku and Rammasun of 2008, were selected on the basis of their strength and wide azimuthal coverage from the seismic array. To track the source of DF microseisms, f-k analysis was applied to the KSRS data to estimate the back azimuth of the 0.2–0.7 Hz noise field (DF microseisms). These computed back azimuths show good agreement with the known values to the centers of the NW Pacific typhoons. This clearly indicates that these typhoons were the main source of microseisms during their passing. The seismic phases in our DF microseism band are investigated with the phase velocities from our f-k analysis. The estimated horizontal phase velocities range from 3.2 to 3.8 km/s, with an average of about 3.5 km/s. This indicates that the major phases of the observed DF microseisms are surface waves consisting of mostly P-SV Mode 1 and Mode 2—in amplitude ratio A1/A2 ≈ 1/3—and possibly some Mode 3.