Use of ANSS Strong-Motion Data to Analyze Small Local Earthquakes

Use of ANSS Strong-Motion Data to Analyze Small Local Earthquakes Plots (from Pankow et al., 2007) showing the distribution, as a function of distance, magnitude, and site response unit (see key) of all measurable arrival times for P-waves (left) and S-waves (right) recorded by accelerometers from 31 earthquakes in the western Salt Lake Valley. The dashed line at 15 km distance envelops those picks (< 15 km) that could improve focal-depth control.
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Traditionally, accelerometers have been used for recording triggered strong-ground motions from earthquakes with M > 4. The data from these instruments have been primarily used by engineers for building design and by seismologists modeling fault rupture histories. Although older generation strong-motion instruments were “incapable of recording small or distant earthquakes” (USGS, 1999, p. 12), advances in accelerometer and digital recording technology have greatly reduced this limitation. Following the 2002 Denali Fault earthquake we learned that modern continuously telemetered strong-motion instruments provide valuable recordings of some teleseismic earthquakes [Pankow et al., 2004]. Since then, we have learned that these instruments also provide valuable recordings of small (0.5 < M < 4) local earthquakes. Hundreds of modern strong- motion instruments have been deployed during the last decade as part of the U.S. Geological Survey Advanced National Seismic System (ANSS). Using the archive of continuous data from University-of-Utah-operated ANSS stations stored at the IRIS DMC, we determined the magnitude and distance ranges over which first arrivals could be successfully picked from accelerometers located on both rock and soil in northern Utah (see figure). The earthquake dataset consisted of 31 earthquakes (M 0.5 to M 3.2) located in the Salt Lake Valley. Somewhat surprisingly, earthquakes as small as M 2 are well-recorded on accelerometers to epicentral distances of 35 to 45 km at soil sites and 70 km at rock sites. ANSS accelerometers are collecting a rich new dataset, much of which is being archived at the IRIS DMC. This dataset is important not just for recording “the big one” and for strong- motion seismology, but also for studies of teleseisms, structure, and local seismicity.
</p><p>References
</p><p>Pankow, K.L., W.J. Arabasz , S.J. Nava, and J. C. Pechmann, Triggered seismicity in Utah from the 3 November 2002 Denali fault earthquake, Bull. Seismol. Soc. Amer., 94, S332-S347, 2004.
</p><p>Pankow, K.L., J. C. Pechmann, and W.J. Arabasz , Use of ANSS strong-motion data to analyze small local earthquakes, Seismol. Res. Lett., 78, 369-374,2007.
</p><p>USGS, An assessment of seismic monitoring in the United States: Requirement for an Advanced National Seismic System: U.S. Geological Survey Circular 1188, 55 p., 1999.
</p><p>Acknowledgements: This project was supported by the U.S. Geological Survey, Department of the Interior, under USGS award number 04HQAG0014, and by the State of Utah under a line-item appropriation to the University of Utah Seismograph Stations.</p>

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