A Central Brazil GT5 Event
Abstract
Ground-truth (GT) events, accurately located with a precision of 5 km (GT5 event) and associated travel times to regional stations are important in developing precise velocity models. The low Brazilian seismicity, with only three continental earthquakes of magnitude five in the last three decades, and the low number of seismic stations explain the difficulty to detect events at regional distances. In the world maps of GT events, Brazil appears almost empty. In Stable Continental Interiors, like Brazil, it is difficult to find an event fulfilling all the GT5 prerequisites, particularly in respect with the number of picked phases and azimuthal gaps. Recently PTS-CTBTO has organized meeting and workshops to encourage seismologists from South and Central America to cooperate with the work of identifying GT5 events in these countries, with a goal of developing a 3-dimentional velocity model for this part of the globe not covered yet like Europe and North America. As a result we studied a recent magnitude 5 event in Central Brazil detected by few regional stations. Aftershock studies with local stations, showed a fault 5 km long. Taking the mainshock epicenter as the center of fault the maximum error would be minimal, 2.5 km, assuming the events were located with zero uncertainty. The parameters depth and origin time source were precisely determined using correlations between waveforms of six events and stations corrections. The event magnitudes range from 3.5 to 5.0 (mainshock, taken as reference event) recorded by regional and local stations. Events recorded at local and regional stations were used to determine the regional station corrections. These events were located only with data from local stations, assigning to the regional stations P and S phases zero weight in order to determine residuals for each regional stations used. The stations corrections were taken as the average of the residuals at each station. Precise pickings of P and S phases for the mainshock were determined using waveforms correlation between different events recorded in the same station in such way that you may read a poor phase based in clear one of similar event. This was based on the fact that events with sources close to each other have more or less the same seismic signature, i.e. have similar waveforms. The differences in size of the seismic sources that causes differences in spectral content were compensated by using the same band pass-filter for both events. This GT5 event in Central Brazil was recorded at more than 15 stations within 15 degrees distance and will help constrain 3D models in South America.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2013
- Bibcode:
- 2013AGUSM.S33C..07B
- Keywords:
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- 7219 SEISMOLOGY / Seismic monitoring and test-ban treaty verification;
- 7230 SEISMOLOGY / Seismicity and tectonics