Audible acoustics from low-magnitude fluid-induced earthquakes in Finland

Oliver D Lamb; Jonathan M Lees; Peter E Malin; Tero Saarno

doi:10.1038/s41598-021-98701-6

Audible acoustics from low-magnitude fluid-induced earthquakes in Finland

Sci Rep. 2021 Sep 28;11(1):19206. doi: 10.1038/s41598-021-98701-6.

Authors

Oliver D Lamb¹, Jonathan M Lees², Peter E Malin^{3

4}, Tero Saarno⁵

Affiliations

¹ Department of Geological Sciences, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA. olamb@email.unc.edu.
² Department of Geological Sciences, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
³ Earth and Ocean Sciences, Nicholas School of the Environment, Duke University, Durham, NC, USA.
⁴ ASIR Advanced Seismic Instrumentation and Research, Raleigh, NC, USA.
⁵ St1 Deep Heat Oy, Helsinki, Finland.

Abstract

Earthquakes are frequently accompanied by public reports of audible low-frequency noises. In 2018, public reports of booms or thunder-like noises were linked to induced earthquakes during an Engineered Geothermal System project in the Helsinki Metropolitan area. In response, two microphone arrays were deployed to record and study these acoustic signals while stimulation at the drill site continued. During the 11 day deployment, we find 39 earthquakes accompanied by possible atmospheric acoustic signals. Moment magnitudes of these events ranged from [Formula: see text] to 1.87 with located depths of 4.8-6.5 km. Analysis of the largest event revealed a broadband frequency content, including in the audible range, and high apparent velocities across the arrays. We conclude that the audible noises were generated by local ground reverberation during the arrival of seismic body waves. The inclusion of acoustic monitoring at future geothermal development projects will be beneficial for studying seismic-to-acoustic coupling during sequences of induced earthquakes.