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The Far-Field Effect of Large Earthquakes in GPS Time-Series

Zachary M. Young, & Corné W. Kreemer

Published August 15, 2017, SCEC Contribution #7784, 2017 SCEC Annual Meeting Poster #095

The proper identification of earthquake-related offsets in GPS time-series is important, not only to characterize the earthquake and the elastic medium, but also because other parameters, most notably the rate, may be biased when offsets are not estimated or when offsets are estimated where there are none. This is particularly an issue for places where the tectonic rate is low, such as the Colorado Plateau, which may have been affected by the 2010 El Mayor-Cucapah event. The time-series analysis done by the Nevada Geodetic Laboratory (NGL) includes offset estimation at stations within a certain distance from an earthquake with a certain magnitude. The empirical relationship used does not include azimuthal dependence. Here, we employ statistical tests (such as the F-test) to determine which components of stations at various distances require an offset at the time of recent large earthquakes in California. We find statistically significant offsets in certain components at distances larger than those considered in NGL’s algorithm. The flip side is that for other components we find no offsets at distances identified by the algorithm. We clearly see the areas that lie in the direction of the events’ nodal planes as those where station time-series have no significant offset in any direction. We employ the same analysis as done for co-seismic offsets to the possible change in velocity after the earthquakes, such as we see in many far-field stations after El Mayor-Cucapah. The findings typically agree with those from the offset analysis.

Key Words
GPS time-series earthquakes

Young, Z. M., & Kreemer, C. W. (2017, 08). The Far-Field Effect of Large Earthquakes in GPS Time-Series. Poster Presentation at 2017 SCEC Annual Meeting.

Related Projects & Working Groups
Tectonic Geodesy