Modeling of the velocity structure beneath Ohio based on explosions from mines in Ohio and neighboring states
Tsigabu Gebrehewit and David Steer
University of Akron
The Ohio Seismic Network (Ohioseis) is providing invaluable data being used to improve understanding of the crustal and upper mantle velocity structure beneath Ohio. Waveform data are being analyzed from 12 stations that were selected based on their spatial distribution and precision (most have GPS time lock for the period April to August, 2001). The mid-continent of the US (including Ohio) are known to be seismically inactive. Therefore, waveforms that originate from limestone/dolomite and coal strip mines are used in this study when they are recorded at multiple stations. Actual mine-related waveforms are identified using an amplitude-based trigger and screened using a temporal criterion. Pre-processing of data include (1) band pass filtering of the selected waveforms, (2) cross-correlation of waveforms from different seismic stations to search for explosions recorded in multiple stations, (3) identification of P and S wave arrivals based on signal-to-noise ratio, phase character and time lag. Differential S-P arrival times from the filtered and screened waveforms are used to determine locations. The potential source sites are compared to known quarry sites for Ohio and adjacent states. Approximately thirty mine sites are being used for the travel time inversion modeling used in this research. This research seeks to determine if lateral velocity anomalies exist in the crust and upper mantle beneath Ohio and to what extent such anomalies are related to known tectonic boundaries. The present understanding of the basement complex is based largely on interpretations of aeromagnetic and gravity data combined with sporadic deep seismic reflection profiles. The final output of this study will be compared with available velocity models from previous studies that were based on teleseismic and surface wave data.
Figure 1. Location map for stations used from the OhioSeis Network.
Last update March 06, 2003