Publications

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2016
Melgar, D, Allen RM, Riquelme S, Geng JH, Bravo F, Baez JC, Parra H, Barrientos S, Fang P, Bock Y, Bevis M, Caccamise DJ, Vigny C, Moreno M, Smalley R.  2016.  Local tsunami warnings: Perspectives from recent large events. Geophysical Research Letters. 43:1109-1117.   10.1002/2015gl067100   AbstractWebsite

We demonstrate a flexible strategy for local tsunami warning that relies on regional geodetic and seismic stations. Through retrospective analysis of four recent tsunamigenic events in Japan and Chile, we show that rapid earthquake source information, provided by methodologies developed for earthquake early warning, can be used to generate timely estimates of maximum expected tsunami amplitude with enough accuracy for tsunami warning. We validate the technique by comparing to detailed models of earthquake source and tsunami propagation as well as field surveys of tsunami inundation. Our approach does not require deployment of new geodetic and seismic instrumentation in many subduction zones and could be implemented rapidly by national monitoring and warning agencies. We illustrate the potential impact of our method with a detailed comparison to the actual timeline of events during the recent 2015 M(w)8.3 Illapel, Chile, earthquake and tsunami that prompted the evacuation of 1 million people.

2015
Melgar, D, Crowell BW, Geng JH, Allen RM, Bock Y, Riquelme S, Hill EM, Protti M, Ganas A.  2015.  Earthquake magnitude calculation without saturation from the scaling of peak ground displacement. Geophysical Research Letters. 42:5197-5205.   10.1002/2015gl064278   AbstractWebsite

GPS instruments are noninertial and directly measure displacements with respect to a global reference frame, while inertial sensors are affected by systematic offsetsprimarily tiltingthat adversely impact integration to displacement. We study the magnitude scaling properties of peak ground displacement (PGD) from high-rate GPS networks at near-source to regional distances (similar to 10-1000 km), from earthquakes between M(w)6 and 9. We conclude that real-time GPS seismic waveforms can be used to rapidly determine magnitude, typically within the first minute of rupture initiation and in many cases before the rupture is complete. While slower than earthquake early warning methods that rely on the first few seconds of P wave arrival, our approach does not suffer from the saturation effects experienced with seismic sensors at large magnitudes. Rapid magnitude estimation is useful for generating rapid earthquake source models, tsunami prediction, and ground motion studies that require accurate information on long-period displacements.