Data Event Response to the January 23, 2018 M 7.9 Earthquake 280km SE of Kodiak, Alaska

Written by David Phillips and Beth Bartel
23 January 2018

Event Summary

A Mw 7.9 earthquake occurred at 09:31:42 UTC on January 23, 2018 (00:31:42 local), 280km SE of Kodiak, Alaska. For more information, see the USGS Earthquake Hazards Program event page.

UNAVCO Response

GPS Real-time Data Streams
Signals from this event were recorded by 16 UNAVCO GPS stations that were streaming high rate (1-sps / 1 Hz) data in real time (Figures 2 and 3). These data allowed peak ground displacements (PGD) to be calculated automatically from the displacement traces within seconds of the earthquake (Figure 3), with a magnitude derived from inverting the PGDs of M7.8. Note: figures and findings are preliminary and subject to revision.

GPS Real-time Stations Used
AC67 AC20 AC44 ATW2 AC53 AC11 AB43 AB44 AB50 AV34 AV39 AV26 AB53 AB49 AV24 AV09 AB18 NEAH P401

GPS Data - Custom Downloads for Post Processing
UNAVCO is downloading high-rate 1-sps (1 Hz) and 5-sps (5 Hz) GPS/GNSS data from Plate Boundary Observatory stations within 2,000 km of the epicenter for a 6-hour time window around the event (± 3 hours). A map of GPS stations being downloaded is shown in Figure 2. These data will be available from the UNAVCO high rate data ftp site.

GPS Displacements
Tom Herring (MIT), the GAGE GPS Analysis Center Coordinator (ACC), has estimated preliminary coseismic offsets associated with the 2018-01-23 M7.9 Kodiak, AK earthquake. Individual station offsets are tabulated in a “rapid" event (*.EVT) file available from the event products ftp site. The horizontal displacements in this event file are plotted in Figure 9. As more data become available, the ACC will also produce a “final” offset solution as well as offsets estimated from Kalman filter time series analyses. Final and Kalman filter offset files will be added to the event file at the event products ftp site.

Borehole Strainmeter Data
UNAVCO has produced a fully processed 1-sps borehole strainmeter (BSM) dataset spanning the time period of this event, available from the PBO borehole strainmeter event response page.