Abstract
We have developed a new continuous monitoring system based on small seismic sources and distributed acoustic sensing (DAS). The source system generates continuous waveforms with a wide frequency range. Because the signal timing is accurately controlled, stacking the continuous waveforms enhances the signal-to-noise ratio, allowing the use of a small seismic source to monitor extensive areas (multi-reservoir). Our field experiments demonstrated that the monitoring signal was detected at a distance of ~ 80 km, and temporal variations of the monitoring signal (i.e., seismic velocity) were identified with an error of < 0.01%. Through the monitoring, we identified pore pressure variations due to geothermal operations and rains. When we used seafloor cable for DAS measurements, we identified the monitoring signals at > 10 km far from the source in high-spatial resolution. This study demonstrates that multi-reservoir in an extensive area can be continuously monitored at a relatively low cost by combining our seismic source and DAS.
Highlights
We have developed a new continuous monitoring system based on small seismic sources and distributed acoustic sensing (DAS)
We have developed continuous and low-cost monitoring system for multi-reservoir distributed in extensive area (Fig. 10)
This study confirmed that the monitoring signal propagates as far as ~ 80 km via onshore seismometers and longer than 10 km via DAS for the seafloor cable (Fig. 5)
Summary
We have developed a new continuous monitoring system based on small seismic sources and distributed acoustic sensing (DAS). Analyzing the ambient noise in continuous seismometer records shows spatio-temporal velocity variations for monitoring p urposes[12,17,18,19]; in this approach, ambient noise is used to derive virtual active-source seismic data[20]. This method has been used to document crustal-scale seismic velocity variations near earthquake faults and volcanoes[12,21,22,23]. These ambient noise characteristics are variable for higher frequencies, strongly influenced by human activities and weather events
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