Observations of the Prompt Elastogravity Signals Generated by the 2018/01/23 Gulf Of Alaska Earthquake Traveling Across the Alaska Seismic Network
Abstract
The recent first observations of the prompt elastogravity signals preceding direct seismic waves raised the question of their detectability for earthquakes smaller than the 2011 Mw=9.1 Tohoku subduction earthquake. As these tiny signals are close to the ambient and/or instrumental noise level, we expect the signal-to-noise ratio to be enhanced by stacking techniques, allowing for detection of smaller earthquakes. The recent 2018/01/23 Mw=7.9-8 Off-Alaska earthquake has a seismic moment about 50 times smaller than the Tohoku earthquake, but benefits from the high density of the broadband seismic network in Alaska. Moreover, the strike-slip focal mechanism of this earthquake makes it, in theory, a more favorable case for elastogravity signal detection than a shallow-dipping subduction earthquake of same magnitude. Thanks to the existing network combined with the recent USArray deployment, this area is homogeneously covered by high quality seismic stations, offering the possibility to track signals far below the noise level of an individual (even excellent) very broadband station. We will show here that standard stacking techniques undoubtedly reveal the existence of the elastogravity signals with a high signal-to-noise ratio. Detection can be even improved by weighting the stack by the ratio between the expected signal amplitude (computed from the known focal mechanism, magnitude, and source time function of the event) and the square of the noise amplitude of each station. In addition to the detection itself, we show that the numerical simulation of the stack is in very good agreement with the data provided that the signals are computed with the adequate earthquake source parameters. From a monitoring perspective, these findings confirm the strong potential of prompt elastogravity signals for characterizing first order key source parameters (lower bound of the magnitude and focal mechanism) in the few minutes following the onset of a large event.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.S33A..02V
- Keywords:
-
- 7230 Seismicity and tectonics;
- SEISMOLOGYDE: 7240 Subduction zones;
- SEISMOLOGYDE: 7294 Seismic instruments and networks;
- SEISMOLOGY