Characteristics of Airplanes and Helicopters Recorded by a Dense Seismic Array Near Anza California

Abstract

We observe frequent air traffic events in continuous seismic waveforms recorded for about 30 days by 1,108 vertical geophones in a tight array on the San Jacinto fault zone. The waveforms of the air traffic events resemble tremor or collections of small earthquakes. However, time‐frequency analysis reveals clear Doppler effects that can be modeled with basic equations and fitted well with parameters corresponding to airplanes and helicopters. The flying traces can be inverted by fitting the parameters at each station across the entire array. About 31 air traffic events are detected per day in the relatively remote study area, with peak activity from about 8:00 to 18:00 and significantly fewer events between 23:00 and 4:00 local time. The average event duration is about 200 s, so they cover together >7% of the day. To estimate the total time covered by earthquakes, we derive a scaling relation logτ(M) = 0.41M + 0.89 between earthquake duration and magnitudes using data of 266 earthquakes in the magnitude range 0 ≤ M ≤ 3. The results indicate that in most places, the duration of air traffic events is likely to exceed considerably the total time covered by earthquakes.

Impact of Nested Moisture Cycles on Coastal Chalk Cliff Failure Revealed by Multiseasonal Seismic and Topographic Surveys

“…We considered only events detected by at least three seismic stations (minimum required to locate an event), within 11 s (maximum time required for a seismic signal to travel through the network). All admitted events were manually checked for plausibility based on (i) consistent amplitude decrease across the network as expected for a local seismic source; (ii) consistent signal arrival time delay across the network, indicative of a local source predominantly emitting surface waves; (iii) an emergent onset and slow decay of the signal, as reported for many hillslope mass wasting processes (Dietze, Mohadjer, et al, 2017;Helmstetter & Garambois, 2010;Hibert et al, 2011); (iv) absence of earthquake-like distinct arrivals of different wave types; and (v) absence of tremor-like frequency patterns, often associated with overhead passage of aircraft (Meng & Ben-Zion, 2018).…”

Semiautomated Estimates of Directivity and Related Source Properties of Small to Moderate Southern California Earthquakes Using Second Seismic Moments

“…A bandpass filtering with corner frequencies at 0.5 and 20 Hz is then performed on the waveforms to suppress the noise associated with ocean tides, wind, and various other natural and anthropogenic noise sources (e.g. Hillers et al, ; Inbal et al, ; Johnson et al, ; Meng & Ben‐Zion, ). We primarily use the transverse component to get relatively clean SH wave data and the vertical component to get P wave data.…”

Imaging subsurface structures in the San Jacinto fault zone with high-frequency noise recorded by dense linear arrays

“…Systematic examination of data recorded at other days shows that this HF noise is persistent throughout the year with daily fluctuations involving primarily increased activity during daytime. The sources of this HF excitation are not fully understood and could include air-traffic, car-traffic and train events (Inbal et al 2018;Meng & Ben-Zion 2018). However, the DW and JF arrays are in very remote areas with no significant roads within 10 km of either site.…”