Magnitude Estimation for Earthquake and Tsunami Early Warning Systems

In this study, different magnitude estimation methods were investigated for application to earthquake early warning (EEW) and tsunami early warning systems. This integrated study is divided into two main parts. First, I used strong motion accelerograms recorded by borehole and surface stations from the Kiban Kyoshin network (KiK-net) for Japanese earthquakes with moment magnitude (M) ≥ 5.0 in order to develop ground motion prediction equations (GMPEs). I developed new GMPEs for peak ground acceleration (PGA) and peak ground velocity (PGV) using two different catalogs. The first catalog included earthquakes with 5.0 ≤ M ≤ 8.1 from 1998-2010. In order to improve the determination of attenuation parameters and magnitude scaling, the second catalog included earthquakes with 5.0 ≤ M ≤ 9.0 from 1998-2011, which increased the time period by only one year but added approximately twice as much data to the first catalog. The GMPEs were used to estimate the magnitude from PGA values (Mpga) and from PGV values (Mpgv) for those events in the borehole and surface databases with at least 20 available records. The results confirmed that Mpga and Mpgv strongly correlate with the moment magnitude of the event. In addition, I studied the site effect terms in the GMPEs using the shear wave velocity in the uppermost 30 meters (VS30). It was found that correcting for VS30 improved the accuracy of magnitude estimates from surface recordings, particularly for Mpgv. Incorporation of this parameter into the GMPEs can provide a more accurate estimate of the earthquake magnitude in EEW systems. The GMPEs also were used to estimate the magnitude of the M9.0 Tohoku event and those estimates were compared with the magnitude estimates provided by the existing EEW system in Japan. I demonstrate that, unlike the estimates provided by the existing EEW system in Japan, the magnitude estimates from GMPEs do not saturate. The results demonstrate that Mpgv from borehole recordings had the smallest standard deviation among the estimated magnitudes and produced more stable and robust magnitude estimates. Based on this observation, I propose the incorporation of borehole recordings into EEW systems. This method can improve the existing EEW system in Japan or other regions that have a dense seismic network. In the second part of this thesis, the displacement spectra of the strong ground motion recordings were used to directly estimate the magnitude of Japanese earthquakes with 4.5 ≤ M ≤ 9.0, 2000 to 2011, using the first available data provided by the KiK-net and Kyoshin network stations. The source parameters were determined using the inversion of displacement spectra for available P- and S-waves windows assuming the Brune source model. I tested the application of a fixed low-cut filter, and found that it decreases the accuracy of magnitude estimation for large events (M \u3e 7.0). As a result, instead of a fixed low-cut filter I applied a frequency bandwidth cutoff based on a signal-to-noise ratio criterion. The results showed that magnitude estimation using the strong motion recordings from the closest station to the source of the event provides a good early estimate for the final size of the event, which can reduce the time required to calculate final magnitude and hence provides a longer warning time (from a few seconds to a few minutes). The results also indicated that the predicted magnitude based on the P-wave window (MP) provides a longer warning time, but with a larger uncertainty, in comparison to the estimation based on the S-wave window (MS). The magnitude estimate based on inversion of the displacement spectra is independent of magnitude scaling relationships, as is the case with magnitude vs. early P-wave parameter relationships or GMPEs, because it determines the moment magnitude from the estimated source parameters directly from the displacement spectra. Therefore, this method can be used in regions with sparse seismic networks where historic recordings of strong ground motion from potentially damaging earthquakes are not available to develop an empirical relationship, such as the Cascadia region of North America

Near real-time GPS applications for tsunami early warning systems

GPS (Global Positioning System) technology is widely used for positioning applications. Many of them have high requirements with respect to precision, reliability or fast product delivery, but usually not all at the same time as it is the case for early warning applications. The tasks for the GPS-based components within the GITEWS project (German Indonesian Tsunami Early Warning System, Rudloff et al., 2009) are to support the determination of sea levels (measured onshore and offshore) and to detect co-seismic land mass displacements with the lowest possible latency (design goal: first reliable results after 5 min). The completed system was designed to fulfil these tasks in near real-time, rather than for scientific research requirements. The obtained data products (movements of GPS antennas) are supporting the warning process in different ways. The measurements from GPS instruments on buoys allow the earliest possible detection or confirmation of tsunami waves on the ocean. Onshore GPS measurements are made collocated with tide gauges or seismological stations and give information about co-seismic land mass movements as recorded, e.g., during the great Sumatra-Andaman earthquake of 2004 (Subarya et al., 2006). This information is important to separate tsunami-caused sea height movements from apparent sea height changes at tide gauge locations (sensor station movement) and also as additional information about earthquakes' mechanisms, as this is an essential information to predict a tsunami (Sobolev et al., 2007). <br><br> This article gives an end-to-end overview of the GITEWS GPS-component system, from the GPS sensors (GPS receiver with GPS antenna and auxiliary systems, either onshore or offshore) to the early warning centre displays. We describe how the GPS sensors have been installed, how they are operated and the methods used to collect, transfer and process the GPS data in near real-time. This includes the sensor system design, the communication system layout with real-time data streaming, the data processing strategy and the final products of the GPS-based early warning system components

Feasibility of Tsunami Early Warning Systems for small volcanic islands

Abstract. This paper investigates the feasibility of Tsunami Early Warning Systems for small volcanic islands focusing on warning of waves generated by landslides at the coast of the island itself. The critical concern is if there is enough time to spread the alarm once the system has recognized that a tsunami has been generated. We use the results of a large scale physical model experiment in order to estimate the time that tsunamis take to travel around the island inundating the coast. We discuss how and where it is convenient to place instruments for the measurement of the waves

HySEA: An operational GPU-based model for Tsunami Early Warning Systems

HySEA numerical model for the simulation of earthquake generated tsunamis is presented. The initial sea surface deformation is computed using Okada model. Wave propagation is computed using nonlinear shallow water equations in spherical coordinates, where coastal inundation and run-up are suitable treated in the numerical algorithm. Generation, propagation and inundation phases are all integrated in a single code and computed coupled and synchronously when they occur at the same time. Inundation is modelled by allowing cells to dynamically change from dry to wet and reciprocally when water retreats from wetted areas. Special effort is made in preserving model well-balanced (i.e. capturing small perturbations to the steady state of the ocean at rest). The GPU model implementation allows faster than real time (FTRT) simulation for real large-scale problems. The large speed-ups obtained make HySEA code suitable for its use in Tsunami Early Warning Systems. The Italian TEWS at INGV (Rome) has adopted HySEA GPU code for its National System. The model is verified by hindcasting the wave behaviour in several benchmark problems. Numerical results for an earthquake-generated tsunami in the Mediterranean Sea is presented and computing time analysed. The interest of using higher order methods, analysing numerical schemes from first order up to order five, in the context of TEWS, is also addressed. Tsunami codes do not usually use higher than second order methods. It is demonstrated that this should idea should be revised.This research has been partially supported by the Junta de Andalucía research project TESELA (P11-RNM7069), the Spanish Government Research project HySEA2 (MTM2009-11923) and Universidad de Málaga, Campus de Excelencia Internacional Andalucía Tech. The multi-GPU computations were performed at the Laboratory of Numerical Methods (University of Malaga)

Long-period ocean sound waves constrain shallow slip and tsunamis in megathrust ruptures

Great earthquakes along subduction-zone plate boundaries, like the magnitude 9.0 Tohoku-Oki, Japan, event, deform the seafloor to generate massive tsunamis. Tsunami wave heights near shore are greatest when excitation occurs far offshore near the trench, where water depths are greatest and fault slip is shallow. Unfortunately the rupture process there is poorly constrained with land-based geodetic and even seafloor deformation measurements. Here we demonstrate, through dynamic rupture simulations of the Tohoku event, that long-period sound waves in the ocean, observable with ocean-bottom pressure sensors and/or seismometers, can resolve the shallow rupture process and tsunami excitation near the trench. These waves could potentially be used to improve local tsunami early warning systems

The Tsunami Assessment Modelling System by the Joint Research Centre

The Tsunami Assessment Modeling System was developed by the European Commission, Joint Research Centre, in order to serve Tsunami early warning systems such as the Global Disaster Alerts and Coordination System (GDACS) in the evaluation of possible consequences by a Tsunami of seismic nature. The Tsunami Assessment Modeling System is currently operational and is calculating in real time all the events occurring in the world, calculating the expected Tsunami wave height and identifying the locations where the wave height should be too high. The first part of the paper describes the structure of the system, the underlying analytical models and the informatics arrangement; the second part shows the activation of the system and the results of the calculated analyses. The final part shows future development of this modeling tool.JRC.G.2-Support to external securit

Large-scale numerical modeling of hydro-acoustic waves generated by tsunamigenic earthquakes

Abstract. Tsunamigenic fast movements of the seabed generate pressure waves in weakly compressible seawater, namely hydro-acoustic waves, which travel at the sound celerity in water (about 1500 m s−1). These waves travel much faster than the counterpart long free-surface gravity waves and contain significant information on the source. Measurement of hydro-acoustic waves can therefore anticipate the tsunami arrival and significantly improve the capability of tsunami early warning systems. In this paper a novel numerical model for reproduction of hydro-acoustic waves is applied to analyze the generation and propagation in real bathymetry of these pressure perturbations for two historical catastrophic earthquake scenarios in Mediterranean Sea. The model is based on the solution of a depth-integrated equation, and therefore results are computationally efficient in reconstructing the hydro-acoustic waves propagation scenarios

Numerical tool for tsunami risk assessment in the southern coast of Dominican Republic

The southern coast of Dominican Republic is a very populated region, with several important cities including Santo Domingo, its capital. Important activities are rooted in the southern coast including tourism, industry, commercial ports, and, energy facilities, among others. According to historical reports, it has been impacted by big earthquakes accompanied by tsunamis as in Azua in 1751 and recently Pedernales in 2010, but their sources are not clearly identified. The aim of the present work is to develop a numerical tool to simulate the impact in the southern coast of the Dominican Republic of tsunamis generated in the Caribbean Sea. This tool, based on the Tsunami-HySEA model from EDANYA group (University of Malaga, Spain), could be used in the framework of a Tsunami Early Warning Systems due the very short computing times when only propagation is computed or it could be used to assess inundation impact, computing inundation with a initial 5 meter resolution. Numerical results corresponding to three theoretical sources are used to test the numerical tool.This research has been partially supported by the Spanish Government Research project SIMURISK (MTM2015-70490-C2-1-R), the Junta de Andalucía research project TESELA (P11-RNM7069), and Universidad de Málaga, Campus de Excelencia Internacional Andalucía Tech. The GPU and multi-GPU computations were performed at the Unit of Numerical Methods (UNM) of the Research Support Central Services (SCAI) of the University of Malaga