Ground Motion Estimates in Earthquake Early Warning: Performance with Global Seismic and Geodetic Data Set
Abstract
Geodetic earthquake early warning (EEW) algorithms are designed to complement existing point-source seismic systems by estimating fault-finiteness and unsaturated moment magnitude for the largest, most damaging earthquakes. Because large earthquakes are rare and real-time geodetic monitoring is relatively young, however, demonstrating the differential accuracy of ground motion estimates from seismic and geodetic warnings is difficult. Here, we quantify the timeliness and accuracy of seismic and geodetic magnitude and ground motion EEW alerts by testing a suite of large (M>6) earthquakes worldwide. First, we replay seismic data from each earthquake through the ElarmS EEW algorithm in simulated real-time to estimate magnitudes and epicentral locations. We then use the seismic alerts, as well as "perfect" alerts, to trigger the Geodetic Alarm System (G-larmS). At each epoch, G-larmS determines static offsets from the GNSS data based on the provided alert event information, and inverts the offsets for slip on several a priori fault geometries and known faults. ElarmS magnitude errors are -1.0 1.0 and -0.50 0.83 units for the first and final alerts, respectively. ElarmS-triggered G-larmS magnitude errors are -0.62 0.86 and -0.14 0.65 units at the first and final update, respectively. We then calculate shaking intensity (MMI) time series for each station for each event using the simulated real-time solutions. Applying an MMI-threshold approach to accurately characterize warning times on a per-station basis, we classify true positive (TP), true negative (TN), false positive (FP), and false negative (FN) alerts for each event. Using a threshold of MMI 4, ElarmS produces only 12.3% TP alerts with a median warning time of 16.3 20.9 s, while ElarmS-triggered G-larmS results in 44.4% TP alerts with a longer median warning time of 50.2 49.8 s. The number of missed alerts (FN) using a threshold of MMI 3 or MMI 4 is reduced by over 30% with the seismically-triggered geodetic EEW system. Perfectly-triggered G-larmS results provide similar statistics as the triggered system, with slightly longer warning times and more accurate magnitudes. These results demonstrate the added value of a geodetic EEW system, quantifying the gained magnitude accuracy, MMI accuracy, and alert timeliness in an MMI space.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMNH32B..04R
- Keywords:
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- 1240 Satellite geodesy: results;
- GEODESY AND GRAVITYDE: 4331 Disaster relief;
- NATURAL HAZARDSDE: 4335 Disaster management;
- NATURAL HAZARDSDE: 4346 Emergency response and evacuations;
- NATURAL HAZARDS