Towards Bridging the Coseismic and Postseismic Phases: Insights from Imaging Very Early Afterslip of the 2016 Pedernales Earthquake in Ecuador
Abstract
Afterslip is a key postseismic process, and mapping out its spatio-temporal distribution is important for assessing seismic hazard along faults, as well as providing insights into the mechanical properties of faults. Imagery of afterslip estimated with postseismic daily GNSS time series disregard the very early postseismic period that spans the initial minutes to hours after the mainshock. Yet, imaging afterslip during this very early period is important as it brings us closer to the transition between the coseismic and postseismic phases, allows us to resolve the initiation of afterslip, its amplitude, and examine its relation to coseismic slip and longer-term afterslip. In addition, it can potentially improve our ability to forecast the main areas where aftershocks localize.
Here, we present our findings of very early afterslip following the 2016 Mw 7.8 Pedernales earthquake in Ecuador. We used the continuous high-rate GNSS position time series (decimated to 60 seconds) of Twardzik et al. [2019] that span 2.5 minutes to 72 hours after the mainshock. They thus provide postseismic observations during the crucial very early period, and enable us to image afterslip in the first hours after the mainshock. Although the time series are noisy, the inversion strategy that we adopt allows us to obtain a robust image of the spatio-temporal distribution of very early afterslip. Our inversion results suggest a spatial signature of shallow afterslip that is consistent with longer-term afterslip that occurs over the first 30 days. Very early afterslip is also imaged within the mainshock rupture area, that may have been short-lived. Comparisons between very early afterslip and relocated aftershocks show good spatial agreement, consistent with the idea that these aftershocks are mainly driven by afterslip. Importantly, using the first daily GPS position as the origin of the postseismic displacement (here at 12 hours after the earthquake) biases the postseismic geodetic moment, with ~60 % missing over the first 72 hours, that corresponds to ~10 % over the first 30 days. The results of our study demonstrate that inverting high-rate sub-daily GNSS time series spanning the very early postseismic period illuminates additional characteristics of afterslip and improves quantification of postseismic slip budgets on faults.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T11A..02T
- Keywords:
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- 1209 Tectonic deformation;
- GEODESY AND GRAVITY;
- 1294 Instruments and techniques;
- GEODESY AND GRAVITY;
- 8118 Dynamics and mechanics of faulting;
- TECTONOPHYSICS;
- 8120 Dynamics of lithosphere and mantle: general;
- TECTONOPHYSICS