Ground Motion Visualization
Visualization from the January 23, 2018 earthquake
Visualization from the January 24, 2016 Iniskin earthquake
The ground has been cut away to show where the subducting plate is - that's where most earthquake activity of this size usually happens. The town of Kodiak is 183 miles from the epicenter.
Earthquake and Tsunami Timeline
Aftershocks, analyst reviewed and Network Match Filtered
This first plot investigates the seismic sequence of the M7.9 offshore Kodiak earthquake and it’s aftershocks. First, matched filtering is used to search for any evidence of foreshock activity. While many earthquakes do have foreshock sequences, many more do not. There was no seismic activity detected in the week before the mainshock, so it does not appear there were any foreshocks to this earthquake.
Next, matched filtering is used to populate the seismic catalog of the aftershock sequence. Starting with 128 known “template” earthquakes, an additional ~400 earthquakes are uncovered in the first two days of the sequence alone. As more aftershocks are cataloged, the potential to find even more earthquakes during these two days will increase, and the analysis will expand to include more up-to-date results as the coming days pass. Normally, aftershock sequences decay somewhat smoothly over time, and any variation in the decay of the earthquake rate can signify that something funky is going on, like propagating afterslip. In the catalog version of the seismicity rate, some variations are observed (where the red line shows some kinks). However, this should not be interpreted too carefully, as these seismic data are still being processed. In contrast, the matched filter enhanced catalog shows a much smoother decay of the seismicity rate. This is likely because the matched filter technique is finding many of the events missed by the automated processing system.
Here is a map showing analyst reviewed locations (red circles) as well as the Network Matched Filter aftershocks (yellow circles). Also plotted are known faults and seafloor fractures.
Anchorage Strong Motion Map
Largest magnitude Alaska earthquake per year since 1964
Moment Tensor Inversions
(Top left) Distribution of stations used for moment tensor inversion. (Right) Moment tensor solution of offshore Kodiak event using surface waves (75-250 seconds) at regional distances (< 700 km). In black are the recorded data, and synthetics computed using 1D velocity model (Beaudoin et al 1992) are shown in red. Waveform fits are shown only for a subset of stations. For more information on header and labels please see https://scholarworks.alaska.edu/handle/11122/6025. (Bottom left) The depth is estimated by running inversion at multiple depths and finding the solution that gives the least misfit between the recorded seismogram and the synthetics.
Preliminary Coulomb Stress Change on the Aleutian Megathrust
Here, are preliminary Coulomb modeling results for how the M7.9 offshore Kodiak earthquake may have affected the state of stress on the megathrust. The beachball and multi-colored line show the faulting mechanism and the presumed fault plane, respectively. For the beachball, the sense of motion is displayed in the black and white quadrants (the motion along each side of the fault is from the white quadrant and towards the black quadrant). The Coulomb modeling presented here shows that the megathrust near Kodiak is experiencing slightly increased stresses as a result of this earthquake, but the megathrust just east of Kodiak is experiencing slightly decreased stresses as a result of this earthquake. Based on this coulomb stress modeling, it is possible that the regions of the megathrust shaded in warm colors may see heightened earthquake activity as a result of the M7.9 offshore Kodiak earthquake, and the regions shaded in cool colors may see decreased earthquake activity. However, the magnitude of this stress change is small, on the order of 0.1 bar. While some studies have suggested that a 0.1 bar stress increase may be enough to trigger seismicity, the effects will likely be small, if noticeable at all.
Seafloor artistic rendering
IMPORTANT NOTE: the depth of the ocean is exaggerated to show the aftershocks better. Kodiak Island is about 66 times longer than the water depth shown here.