Lab and Field Tests of a Low‐Cost 3‐Component Seismometer for Shallow Passive Seismic Applications.

We performed laboratory tests and field surveys to evaluate the performance of a low‐cost 3‐component seismometer, consisting of three passive electromagnetic spring‐mass sensors, whose 4.5 Hz natural frequency is extended down to 0.5 Hz thanks to hyper damping. Both lab and field datasets show that the −3 dB band of the seismometer ranges approximately from 0.7 to 39 Hz, in agreement with the nominal specifications. Median magnitude frequency response curves obtained from processing field data indicate that lower corner of the −3 dB band could be extended down to 0.55 Hz and the nominal sensitivity may be overestimated. Lab results confirm the non‐linear behavior of the passive spring‐mass sensor expected for high‐level input signals (a few to tens of mm/s) and field data confirm relative timing accuracy is ±10 ms (1 sample). We found that absolute timing of data collected with USB GPS antennas can be affected by lag as large as +0.5 s. By testing two identical units, we noticed that there could be differences around 0.5 dB (i.e., about 6%) between the components of the same unit as well as between the same component of the two units. Considering shallow passive seismic applications and mainly focusing on unstable slope monitoring, our findings show that the tested seismometer is able to identify resonance frequencies of unstable rock pillars and to generate interferograms that can be processed to estimate subsurface velocity variations. Plain Language Summary: This study describes some tests that we did to evaluate a seismometer that is cheaper than similar products on the market. A seismometer is able to sense and collect seismic waves and can be used for several applications including global seismology and hydrocarbon exploration. In our work, we consider passive seismic applications, that is, we focus on seismic waves generated by non‐controlled sources (aka seismic noise). Either the seismic sources are natural or man‐made, a valuable seismometer should allow to record weak signals in a wide frequency band, especially at relatively low frequency (<5 Hz). The results of our tests show that the cheap seismometer can record frequencies down to approximately 0.5 Hz, while, to keep costs low, the highest frequency is limited to about 40 Hz. Field tests show that the seismometers can retrieve information from seismic noise as weak as a few micrometers per second, while lab test with higher inputs shows that the response of the seismometer is dependent upon the input velocity. Overall, we found that the nominal specifications of the seismometers are met, thus the tested unit is a valuable tool for shallow passive‐seismic applications with relatively‐low‐frequency, low‐amplitude signals, and a limited budget. Key Points: A low‐cost 3‐component seismometer has been tested for passive shallow applicationsThe seismometer has non‐linear response for high‐amplitude (mm/s) excitation signalsLab and field tests confirm the −3 dB band ranges from 0.7 to 39 Hz and an offset of about 0.5 s was found in the filed data whose timing was provided by a USB GPS antenna [ABSTRACT FROM AUTHOR]