Research
 

Wavelet Packet Transformation Analysis of Seismic Signals Recorded from a Tornado in Ohio

Vincent, R. K.¹, Zhizhen, Z., Ping, S.², and Shaofen, Z.³
(1) Bowling Green State University, (2) Seismological Bureau of China, (3) Academic Sinica, China

In press 2002, Seismological Society of America Bulletin

Abstract

Seismic signals recorded every 0.1 seconds by four OhioSeis (state network) seismic stations (in Cincinnati, Portsmouth, Columbus, and Bowling Green, Ohio) for two hours before and 30 minutes after a destructive F4 tornado hit a suburb of Cincinnati (Blue Ash) at approximately 0500 hours EST on April 9, 1999, were subjected to wavelet packet transformation analysis and to transient frequency analysis with a Wigner Distribution. In the U. of Cincinnati station data (12 Km from Blue Ash) we found a high-intensity, low-frequency (0.05-0.128 Hz) signal during the reported touchdown, and also the loss of all but the lowest-intensity, higher-frequency signals recorded by the seismometer (maximum of 1.5 Hz) as a possible precursor of the tornado approximately 6 minutes before it hit the ground. This higher frequency loss continued until 14 minutes after the tornado touchdown. In the Portsmouth, Columbus, and Bowling Green station signals we found that the highest correlated matches with the U. of Cincinnati station tornado signal occurred at respective arrival times that agreed with an approximately 1.8 km/sec propagation velocity for this low-frequency, seismic wave. The seismic record from a second F4 tornado in Xenia, Ohio, which occurred on September 20, 2000, was similar to the Blue Ash tornado record, as recorded by the same U. of Cincinnati station, at an 80 Km distance from Xenia.