Document Type

Thesis

Date of Degree Completion

Spring 2018

Degree Name

Master of Science (MS)

Department

Geological Sciences

Committee Chair

Tim Melbourne

Second Committee Member

Breanyn MacInnes

Third Committee Member

Walter Szeliga

Fourth Committee Member

Diego Melgar

Abstract

Tsunami early warning systems currently comprise modeling of observations from the global seismic network, deep-ocean DART buoys, and a global distribution of tide gauges. While these tools work well for tsunamis traveling teleseismic distances, saturation of seismic magnitude estimation in the near field can result in significant underestimation of tsunami excitation for local warning (Wang et al., 2012). Moreover, DART buoy and tide gauge observations cannot be used to rectify the underestimation in the available time, typically 10-20 minutes, before local runup occurs. Real-time GNSS measurements of coseismic offsets may be used to estimate finite faulting within 1-2 minutes and, in turn, tsunami excitation for local warning purposes (Blewitt et al., 2006; Melgar and Bock, 2013; Yue and Lay, 2011). Described here is a tsunami amplitude estimation algorithm, implemented for the Cascadia subduction zone, that uses continuous GNSS position streams to estimate finite faulting. The system is based on a time-domain convolution of fault slip that uses a pre-computed catalog of hydrodynamic Green’s functions generated with the GeoClaw shallow-water wave simulation software and maps seismic slip along each section of the fault to points located off the Cascadia coast in 20m of water depth and relies on the principle of the linearity in tsunami wave propagation. The system draws continuous slip estimates from a message query server (RabbitMQ), convolves the slip with appropriate Green’s functions which are then superimposed to produce wave amplitude at each coastal location. The maximum amplitude and its arrival time are then passed into a database for subsequent monitoring and display. This system was tested with data from a real earthquake for which we have continuous GNSS time series and surveyed runup heights, Tohoku, Japan 2011. This system has been implemented in the CWU Geodesy Lab for the Cascadia subduction zone and will be expanded to the circum-Pacific as real-time processing of international GNSS data streams become available.

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