Evaluating an Earthquake Early Warning System in Utah

Debi Kilb, Emily Morton, Keith Koper, & Relu Burlacu

Submitted September 10, 2023, SCEC Contribution #13075, 2023 SCEC Annual Meeting Poster #019

According to a 2023 FEMA report, Utah has the fourth highest seismic risk among U.S. states—behind only California, Oregon, and Washington—with an annualized earthquake loss estimate of $367 million. This high risk results from the concentration of population and infrastructure along the Wasatch Front. Paleoseismic studies have reported at least 26 M6.5+ earthquakes in the last 6,500 years along the nearby Wasatch fault. The probability of an M6.5+ earthquake along the Wasatch Front in the next 50 years is 43%, and an M7 earthquake on the Salt Lake City segment of the Wasatch fault is expected to cause 2,000–2,500 deaths, 7,400–9,300 serious injuries, and over $33 billion in short-term economic losses. Efforts are underway to mitigate the seismic risk by retrofitting or replacing the 140,000+ unreinforced masonry buildings along the Wasatch Front. The development of an earthquake early warning (EEW) system in Utah presents an opportunity to work in parallel with these efforts, providing mitigation strategies that can be in place within a much shorter time frame (years instead of decades).

In 2022, the State of Utah appropriated funds to study the feasibility of implementing an EEW system in Utah. Our initial findings show that along the Wasatch Front, the existing seismic network density (~90 stations) is adequate for a prototype EEW system to function reliably. The greatest need for a prototype Wasatch Front EEW system is upgraded telemetry to meet typical EEW data latency requirements. A fully functional EEW system, covering the entire Wasatch Front Region, would require about 80 new stations. Assuming an idealized seismograph network along the Wasatch Front region, a four-station detection method that alerts on P waves (Vp of 5.9 km/s), and event depths of 12 km, we assess scenario earthquakes throughout the region. We find that a Wasatch Front EEW system could provide ~15–30 s of warning before noticeable shaking and ~5–15 s of warning before strong shaking. Slightly shorter times are found for a two-station, S wave (Vs of 3.4 km/s) based detection method. Based on historical seismicity, we would expect a Wasatch Front EEW system to alert every 2–3 years on average, although dry spells (periods of no alerts) of 5–10 years could arise. Extending the system beyond the Wasatch Front, where the seismic hazard is lower, would require an additional 118 stations to adequately operate along the entire Intermountain Seismic Belt in Utah.

Key Words
Earthquake Early Warning, Utah, Seismic network, warning times, ShakeAlert

Kilb, D., Morton, E., Koper, K., & Burlacu, R. (2023, 09). Evaluating an Earthquake Early Warning System in Utah. Poster Presentation at 2023 SCEC Annual Meeting.

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