Creating the Virtual Seismologist: developments in ground motion characterization and seismic early warning

The Virtual Seismologist method for earthquake early warning uses a Bayesian approach to find the most probable magnitude and location estimates given the incoming ground motions envelopes from a rupturing earthquake. Ground motion ratios and ground motion envelope attenuation relationships are used to estimate magnitude and epicentral location as early as 3 seconds after the initial P wave detection. The use of prior information distinguishes this method from other proposed methods for seismic early warning. The state of health of the seismic network, previously observed seismicity, fault locations, and the Gutenberg-Richter relationship are the types of prior information useful in resolving trade-offs in the initial source estimates which are unresolved by the limited data. Short-term earthquake forecasts are ideal priors for seismic early warning. Having a high density of stations with real-time telemetry reduces the complexity involved in finding the most probable source estimates and communicating these estimates to early warning subscribers. The benefits of prior information are most evident for regions with low station density. Most early warning studies are focused exclusively on either the source estimation problem, or how subscribers use the warning information. The inclusion of prior information ultimately requires a level of coordination and communication between the network broadcasting the early warning information and the subscribers that is not consistent with this divide. The need for a more integrated approach to seismic early warning which considers the source estimation and user response as interacting and interrelated parts of a single problem is discussed. A parameterization that decomposes observed ground motion envelopes into Pwave, S-wave, and ambient noise envelopes is developed and applied to a large suite of observed ground motion envelopes recorded within 200 km of 2 ! M ! 7.3 Southern California earthquakes. Separate attenuation relationships are developed to describe vi the magnitude, distance, and site dependence of various channels of P- and S-wave envelopes. The P-wave relationships allow the early warning source estimates to be obtained from observed P-wave amplitudes. Aside from early warning applications, these envelope attenuation relationships are used to investigate the average properties of ground motions recorded by the Southern California Seismic Network. Stationspecific amplification factors for 150 Southern California Seismic Network stations were obtained for horizontal and vertical acceleration, velocity, and displacement amplitudes, and are included (Excel format) as external multimedia objects

Characterizing Average Properties of Southern California Ground Motion Amplitudes and Envelopes

We examine ground motion envelopes of horizontal and vertical acceleration, velocity, and filtered displacement recorded within 200 km from southern California earthquakes in the magnitude range 2 5 range typically considered for strong motion attenuation relationships

Acerca de la física y de la evaluación de los sistemas de alerta de terremotos y tsunamis

Editorial: Acerca de la física y de la evaluación de los sistemas de alerta de terremotos y tsunami

Real-time Performance of the Virtual Seismologist Earthquake Early Warning Algorithm in Southern California

The Virtual Seismologist (VS) method is a Bayesian approach to regional network-based earthquake early warning (EEW) that estimates earthquake magnitude, location, and the distribution of peak ground motion using observed ground motion amplitudes, predefined prior information, and appropriate attenuation relationships (Cua 2005; Cua and Heaton 2007). The application of Bayes's theorem in earthquake early warning (Cua 2005) states that the most probable source estimate at any given time is a combination of contributions from prior information (possibilities include network topology or station health status, regional hazard maps, earthquake forecasts, the Gutenberg-Richter magnitude-frequency relationship) and a likelihood function, which takes into account observations from the ongoing earthquake. Prior information can be considered relatively static over the timescale of a given earthquake rupture. The changes in the source estimates and predicted peak ground motion distribution, which are updated each second, are due to changes in the likelihood function as additional arrival and amplitude data become available. The potential use of prior information differentiates the VS approach from other regional, network-based EEW algorithms, such as ElarmS (Allen and Kanamori 2003)

Rapid Source Parameter Estimations of Southern California Earthquakes Using PreSEIS

Earthquake early warning (EEW) systems provide real-time estimates of earthquake source and ground motion parameters to users before strong ground shaking occurs at sites of interest (Kanamori et al. 1997; Kanamori 2005). They make use of the fact that the most destructive ground shaking during an earthquake is caused by S- and surface waves, which travel much slower than P waves and also slower than electromagnetic signals carrying warnings to potential users. Real-time information systems can minimize loss of life and property damage and are therefore an important tool in short-term seismic hazard mitigation and disaster management (Wenzel et al. 2001). If an alarm can be issued seconds before the onset of the strong ground motions, automatic emergency actions can be initiated such as slowing down high speed trains or shutting down computers or gas distribution, for instance (Goltz 2002). EEW systems are of two main types, regional and on-site. The former uses a dense network of seismic stations to locate the earthquake, determine its magnitude, and estimate the ground motion at given sites of interest. The latter uses the observations at a single sensor to estimate the ensuing ground motion at the same site (Kanamori 2005). While regional systems work more accurately, they need more time to estimate earthquake source parameters

New predictive equations and site amplification estimates for the next-generation Swiss ShakeMaps

We present a comprehensive scientific and technical update of the Swiss customization of United States Geological Survey ShakeMap, in use at the Swiss Seismological Service since 2007. The new Swiss ShakeMaps are based on predictive equations for peak ground-motions and response spectra derived from stochastic simulations tailored to Swiss seismicity. Using synthetics allows overcoming the difficulties posed by: (i) the paucity of strong-motion data recordings in Switzerland; (ii) the regional dependence of shear wave energy attenuation and focal depth distribution in the Swiss Alps and foreland; (iii) the depth dependence of stress parameters suggested by macroseismic and instrumental observations. In the new Swiss ShakeMaps, VS,30 is no longer used as proxy for site amplification at regional scale, and is replaced by macroseismic intensity increments for different soil classes, based on the recently revised earthquake catalogue of Switzerland (ECOS-09). The new implementation converts ground-motion levels into macroseismic intensity by means of ground-motion to intensity conversion equations based on the Italian strong-motion and intensity databanks and is therefore well constrained for intensities larger than VII. The new Swiss ShakeMaps show a satisfactory agreement with the macroseimic fields of both large historical events and recent well-recorded earthquakes of moderate magnitude. The new implementation is now fully consistent with the state-of-the-art in engineering seismology in Switzerlan

Feasibility study on earthquake early warning and operational earthquake forecasting for risk mitigation at nuclear power plants

International audienceWithin the framework of the EC-funded project REAKT (Strategies and Tools for Real Time Earthquake Risk Reduction, FP7, contract no. 282862, 2011-2014, www.reaktproject.eu), a task concerns feasibility study and initial implementation of Earthquake Early Warning (EEW) and timedependent seismic hazard analyses aimed at mitigating seismic risk at nuclear power plants (NPPs) in Switzerland. This study is jointly carried out by academic institutions (the Swiss Seismological Service at ETHZ and BRGM) and in cooperation with swissnuclear, the nuclear energy section of swisselectric, an umbrella organisation for the nuclear power plants in Switzerland, which provide about 40% of the electricity needs of the country. Briefly presented in this contribution are the main investigations carried out and results obtained throughout the development of this task, with special focus on: a) evaluating the performances of the selected EEW algorithm (the Virtual Seismologist, VS) in Switzerland and California, in terms of correct detections, false alerts, and missed events; b) embedding the VS algorithm into the earthquake monitoring software SeisComP3 (www.seiscomp3.org) routinely used by the Swiss Seismological Service for earthquake detections and locations; c) customising the User Display (a graphical interface originally developed at the California Institute of Technology (Caltech) during Phase II of the ShakeAlert project in California) for optimised use at Swiss NPPs; d) presenting synthetic time-dependent hazard scenarios for Switzerland and e) attempting to associate the above input data with potential mitigation actions and related cost and benefits for NPPs in Switzerland