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Lessons Learned From the 2018 M7.1 Anchorage, Alaska Earthquake: A Network Operator’s Perspective

On November 30, 2018, a magnitude 7.1 earthquake occurred under the most densely populated area of Alaska. It generated the strongest ground shaking in the greater Anchorage area since the Mw 9.2 1964 Great Alaska earthquake. This earthquake was an intraslab event that ruptured a normal fault in the down-going Yakutat slab between 35 and 55 km depth.

The November 30 earthquake occurred under the most densely instrumented part of the Alaska regional seismic network, including the Anchorage strong motion network - one of the most comprehensive urban networks in the US. Availability of the real-time data ensured timely and accurate reporting of the earthquake location and intensity of the ground shaking that was incorporated into several downstream products. AEC used recorded data from strong motion and broadband stations and felt intensities from DYFI reports to generate ShakeMap. However, the earthquake revealed some issues with the metadata that had to be resolved over the course of the following days and weeks.

The mainshock was followed by a vigorous aftershock sequence. AEC located about 11,000 aftershocks in the first year of the sequence, with an aftershock catalog magnitude of completeness of 1.3. Within a few days of the mainshock, USGS installed ten sites around the epicentral region and in the Kenai Peninsula for aftershock monitoring. The stations were equipped with a combination of strong motion and broadband sensors and cell modems for real-time data delivery and ran for about 6 months. AEC incorporated data from these stations into the aftershock processing, enhancing station coverage in the epicentral region. Due to the large number of aftershocks, routine event analysis fell behind in the early weeks of the sequence, but AEC analysts were able to finish aftershock reviews as seismicity rates subsided.

Recorded data from the Mw 7.1 mainshock and aftershocks are being used by seismological and engineering communities to improve understanding of seismic hazards in southcentral Alaska specifically and in similar tectonic settings more broadly.

Presenting Author: Natalia Ruppert

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