Boreholes: Future-Proofing Infrastructure to Enhance the Capabilities of Geophysical Network Arrays

Over the next decade, advancements in artificial intelligence will raise expectations of minimizing impact to public safety and property associated with earthquakes, tsunamis, volcanoes and landslides. Nascent systems such as Operational Earthquake Forecasting (OEF) will require dense networks of broad dynamic range seismometers and reliable, low-latency data transmission, with Borehole OEF systems delivering the affordability and data quality required for future actionable warnings. Currently, Japan (JAMSTEC) is leading the way toward the development of a cost-effective OEF with a dense national network of high-quality, low-noise borehole seismic systems. The seismic monitoring and research community, through projects such as the Subduction Zone Observatory (SZ4D), could mutually leverage these upgrades to improve the performance of next generation sensor networks and communication infrastructure required for their efforts. To facilitate the design of these next generation seismic monitoring networks, including refurbishment of present networks, a cost/benefit model has been developed for several seismic station noise reduction strategies. The study undertakes a comparison of the amount of noise reduction associated with colocated surface and borehole seismometers in existing networks. Based on our preliminary results, the most cost-effective approach to achieving a better signal to noise for OEF is with dry-cased borehole installations with a minimum depth of 10 m. Building high-quality low-noise seismic stations from scratch is expensive, however updating present sites with boreholes provides a cost-effective method of leveraging the high performance of modern low noise broadband instruments and meeting the needs of OEF and discovery.