SEISMIC SIGNALS OF STORM-GENERATED FLASH FLOODS TRAVELING ALONG BLACK CANYON CREEK, ARIZONA
The seismic portion of the network consisted of twelve short-period stations, each with a three-component Sercel L-22 2-Hz sensor and a RefTek RT 130 digitizer, and one broadband station with a three-component Nanometrics Trillium Compact Posthole 120s sensor and a Nanometrics Centaur digitizer. Two Spypoint Solar trail cameras photographed the creek once per minute during daylight. A Davis Vantage Vue weather station recorded precipitation and windspeed near the network’s center.
Thirteen creek refills were photographed by one or both trail cameras; another seven were inferred by overnight increases in photographed creek level and verified by examination of stream-discharge data from the United States Geological Survey “Agua Fria at Rock Springs” gauge. We present our initial analysis of seismic signals accompanying these events.
Most creek refills generated a pulse of wide-bandwidth seismic noise which rose rapidly to a peak amplitude as the floodcrest approached a station, then decayed to background-noise levels over the course of several hours. The peak signal amplitude typically migrated downstream at an average of roughly 2 m/s. At the seismic stations nearest the creek, this signal was strongest between ~15 and ~85 Hz. More distant stations only observed the lower-frequency portion of this band, and at the farthest station, over 500 meters away from the creek, only the highest-discharge Rosa-induced refill produced a plausibly flood-related signal above background noise. The flood signals were distinct from earthquake, mine-blast, and air- and road-traffic noise in duration, envelope shape, and frequency content. However, rainstorms produced high-amplitude seismic noise over a broad frequency range, obscuring simultaneous flood signals at most seismic stations.