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

Abstract

Advances in seismometry and recording systems have greatly increased the range of signals that can be recorded by strong-motion instruments. This increased range has practical implications for observational weak-motion seismology, as we demonstrate in this study. Analog strong-motion instruments, the most common type in use until the 1990s, had an effective bandwidth from ∼ 0.1–0.2 Hz to 25–50 Hz and a dynamic range of 40 to 60 dB (Heaton et al. 1989; Trifunac and Todorovska 2001). By contrast, modern 16- and 24-bit digital strong-motion instruments have bandwidths from DC to 80 Hz (at 200 sps) and a dynamic range of 90 to 135 dB (Trifunac and Todorovska 2001). Another advance in strong-motion instrumentation during the past decade or so has been the development of recorders that can support continuous digital telemetry of the data. Historically, strong-motion data have been recorded on-site in a triggered mode. The triggers usually are set to record potentially damaging ground motions from moderate to large ( M > 4) local earthquakes. These data are used mostly by engineers for structural design and by seismologists for modeling fault rupture histories. The continuous telemetry of strong-motion data has been driven primarily by the need for reliable near-real-time information on potentially damaging ground shaking (Kanamori et al. 1997). Fortunately, the continuous telemetry also enables the recording of smaller signals that normally would not trigger the strong-motion instruments, which means that the full range of signals recorded by the modern accelerometers and digitizers can be investigated. With the deployment of the Advanced National Seismic System (ANSS; USGS 1999) beginning in the year 2000, the number of modern continuously telemetered strong-motion instruments throughout the United States has increased greatly. Before ANSS, the only dense network of such instruments in the United States was located in southern California, as part …