Source location of volcanic earthquakes and subsurface characterization using fiber-optic cable and distributed acoustic sensing system

Takeshi Nishimura,Mare Yamamoto,Shunsuke Sugimura,Kentaro Emoto,Satoshi Miura,Ayumu Ishikawa,Tsunehisa Kimura,Hisashi Nakahara

doi:10.1038/s41598-021-85621-8

Takeshi Nishimura, Mare Yamamoto + Show 6 more

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https://doi.org/10.1038/s41598-021-85621-8

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Journal: Scientific Reports	Publication Date: Mar 18, 2021
Citations: 37	License type: open-access

Affiliation: Tohoku University, Schlumberger (France)

Abstract

We present one of the first studies on source location determination for volcanic earthquakes and characterization of volcanic subsurfaces using data from a distributed acoustic sensing (DAS) system. Using the arrival time difference estimated from well-correlated waveforms and a dense spatial distribution of seismic amplitudes recorded along the fiber-optic cable, we determine the hypocenters of volcanic earthquakes recorded at Azuma volcano, Japan. The sources are located at a shallow depth beneath active volcanic areas with a range of approximately 1 km. Spatial distribution of the site amplification factors determined from coda waves of regional tectonic earthquakes are well correlated with old lava flow distributions and volcano topography. Since DAS observation can be performed remotely and buried fiber-optic cables are not damaged by volcanic ash or bombs during eruptions, this new observation system is suitable for monitoring of volcanoes without risk of system damage and for evaluating volcanic structures.

Highlights

We present one of the first studies on source location determination for volcanic earthquakes and characterization of volcanic subsurfaces using data from a distributed acoustic sensing (DAS) system
Volcanic earthquakes and tremors that are generated by volcanic fluids are generally not well located because the onsets of P- and S-waves, which are used for standard hypocenter determination for tectonic earthquakes, are often unclear and/or seismic signals oscillate for a long t ime[3,4,5]
Since volcanic subsurfaces consist of pyroclasts, old lava flows, steep valleys eroded by rainfalls and so on, evaluation of the site amplification factor and attenuation factor for seismic wave propagation affects the absolute location of the source[9]

Summary

Introduction

We present one of the first studies on source location determination for volcanic earthquakes and characterization of volcanic subsurfaces using data from a distributed acoustic sensing (DAS) system. Using the arrival time difference estimated from well-correlated waveforms and a dense spatial distribution of seismic amplitudes recorded along the fiber-optic cable, we determine the hypocenters of volcanic earthquakes recorded at Azuma volcano, Japan. The accuracy may not be high because wave propagation is greatly affected by heterogeneous structure beneath the arrays Another way to overcome this difficulty is to use the spatial distribution of the seismic amplitude of volcanic earthquakes and t remors[8]. Seismic interferometry techniques have been developed and applied to volcanic tremor data[10,11,12] In these techniques, cross-correlation functions (CCFs) for seismic waves recorded at several stations are stacked in order to retrieve direct waves propagating from the source location, and the time differences for the peaks of CCFs are used to Scientific Reports | (2021) 11:6319. The large number of channels recorded by DAS improves the sensitivity for detecting earthquakes below the noise level[21]

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