PreSEIS: A Neural Network-Based Approach to Earthquake Early Warning for Finite Faults

The major challenge in the development of earthquake early warning (EEW) systems is the achievement of a robust performance at largest possible warning time. We have developed a new method for EEW—called PreSEIS (Pre-SEISmic)—that is as quick as methods that are based on single station observations and, at the same time, shows a higher robustness than most other approaches. At regular timesteps after the triggering of the first EEW sensor, PreSEIS estimates the most likely source parameters of an earthquake using the available information on ground motions at different sensors in a seismic network. The approach is based on two-layer feed-forward neural networks to estimate the earthquake hypocenter location, its moment magnitude, and the expansion of the evolving seismic rupture. When applied to the Istanbul Earthquake Rapid Response and Early Warning System (IERREWS), PreSEIS estimates the moment magnitudes of 280 simulated finite faults scenarios (4.5≤M≤7.5) with errors of less than ±0.8 units after 0.5 sec, ±0.5 units after 7.5 sec, and ±0.3 units after 15.0 sec. In the same time intervals, the mean location errors can be reduced from 10 km over 6 km to less than 5 km, respectively. Our analyses show that the uncertainties of the estimated parameters (and thus of the warnings) decrease with time. This reveals a trade-off between the reliability of the warning on the one hand, and the remaining warning time on the other hand. Moreover, the ongoing update of predictions with time allows PreSEIS to handle complex ruptures, in which the largest fault slips do not occur close to the point of rupture initiation. The estimated expansions of the seismic ruptures lead to a clear enhancement of alert maps, which visualize the level and distribution of likely ground shaking in the affected region seconds before seismic waves will arrive

Urban Earthquake Risk

The impact of earthquakes in urban areas is a complex problem compounded by multi-hazard and consequential risk issues, enormous inventory of vulnerable physical elements and the attendant socio-economic problems. A review of our state-of-knowledge and applications on the assessment of urban earthquake risk is provided. Rational urban risk predictions and expected losses from major earthquakes in the future serve the basis and also provide strong reasons for the proactive risk mitigation activities

Evaluation and optimization of seismic networks and algorithms for earthquake early warning – the case of Istanbul (Turkey)

Earthquake early warning (EEW) systems should provide reliable warnings as quickly as possible with a minimum number of false and missed alarms. Using the example of the megacity Istanbul and based on a set of simulated scenario earthquakes, we present a novel approach for evaluating and optimizing seismic networks for EEW, in particular in regions with a scarce number of instrumentally recorded earthquakes. We show that, while the current station locations of the existing Istanbul EEW system are well chosen, its performance can be enhanced by modifying the parameters governing the declaration of warnings. Furthermore, unless using ocean bottom seismometers or modifying the current EEW algorithm, additional stations might not lead to any significant performance increase

Modeling the Observed Site Response from Istanbul Strong Motion Network

An extensive site investigation study was carried out in the European side of Istanbul as part of the large-scale microzonation project for the Istanbul Metropolitan Municipality. 2912 borings mostly down to 30m depth with approximately 250m spacing were conducted within an area of 182 sqkm to investigate local site conditions. 55 stations of the Istanbul Rapid Response Network and Ataköy vertical array are located in this area. There have been few small earthquakes in the recent years with local magnitude slightly over M=4. One of these earthquakes took place on 12/3/2008 in Yalova with local magnitude of M=4.8. Vertical array stations at 4 levels (ground surface, at depths of 50m, 75m and 140m) and 23 of the 55 Istanbul Rapid Response Network stations recorded this earthquake. Based on the recorded acceleration time histories on the engineering bedrock at Ataköy vertical array, the remaining recorded acceleration time histories are modeled based on empirical site amplification relationships proposed by Borcherdt (1994) and based on a modified version of Shake91 (Idriss and Sun, 1992). An attempt is also made to model the recorded acceleration time histories during the Mw=7.4, 1999 Kocaeli Earthquake recorded at Ataköy, Fatih and Zeytinburnu stations located in the same area

Selection of ground motion prediction equations for the global earthquake model

Ground motion prediction equations (GMPEs) relate ground motion intensity measures to variables describing earthquake source, path, and site effects. From many available GMPEs, we select those models recommended for use in seismic hazard assessments in the Global Earthquake Model. We present a GMPE selection procedure that evaluates multidimensional ground motion trends (e.g., with respect to magnitude, distance, and structural period), examines functional forms, and evaluates published quantitative tests of GMPE performance against independent data. Our recommendations include: four models, based principally on simulations, for stable continental regions; three empirical models for interface and in-slab subduction zone events; and three empirical models for active shallow crustal regions. To approximately incorporate epistemic uncertainties, the selection process accounts for alternate representations of key GMPE attributes, such as the rate of distance attenuation, which are defensible from available data. Recommended models for each domain will change over time as additional GMPEs are developed

Seismic analysis and retrofitting of an existing R.C. highway bridge: investigation through pseudo-dynamic

The “Retro” TA project funded by the European commission within the Series-project aims at studying numerically and experimentally the seismic behaviour of an old existing reinforced concrete bridge with portal frame piers and the effectiveness of different isolation systems. In particular, an experimental test campaign will be performed at ELSA Laboratory of JRC (Ispra, Italy). Two piers (scale 1:2.5) will be built and tested using the PsD technique with sub-structuring; the modelling of he entire viaduct is considered along with the non-linear behaviour of each pier, due to bending, shear on the transverse beams and strain penetration effect at the column bases. The comprehensive numerical investigations have shown the high vulnerability of the sample bridge. Consequently two isolation systems (yielding-based and friction-based bearings) have been currently designed and characterized. Because the test will start after the summer 2012, in this paper the relevant issues will be here addressed and discussed.JRC.G.5-European laboratory for structural assessmen

Guidelines for harmonized hazard assessment for LP-HC events: STREST Reference Report 2

This report describes the main conclusions of the STREST project (and associated guidelines) to evaluate hazard of Low-Probability High-Consequences (LP-HC) events used to define stress tests for non-nuclear Critical Infrastructures (CIs). Several new approaches have been developed to assess these extreme hazard scenarios and to evaluate the associated uncertainties. This report presents a summary of the developments, results and products issued from Work Package 3 (WP3) of STREST. It is given as a set of “recommendations” for potential users responsible of the estimation of hazard for a particular non-nuclear CI in the European Union and other countries. The methods and guidelines are dedicated to two different target-users: project managers and hazard experts. It poses the main differences with a traditional Probabilistic Hazard Assessment analysis, the benefits and extra challenges, and the particular information requirements for the three selected infrastructure classes covered in STREST. In a simple and understandable manner, it summarizes the principal available tools, the main references and the application examples issued from the project in order to help the users in the realization of theirs studies.JRC.E.4-Safety and Security of Building

Guidelines for stress-test design for non-nuclear critical infrastructures and systems: Applications: STREST Reference Report 5

In the context of the STREST project, an engineering multi-level risk-based methodology to stress test critical non-nuclear infrastructures, named ST@STREST, has been developed. This reference report summarizes ST@STREST framework and its exploratory application to six key representative Critical Infrastructures (CIs) in Europe, exposed to variant hazards, namely: a petrochemical plant in Milazzo, Italy, large dams of the Valais region in Switzerland, hydrocarbon pipelines in Turkey, the Gasunie national gas storage and distribution network in Holland, the port infrastructure of Thessaloniki, Greece and an industrial district in the region of Tuscany, Italy. According to the characteristics of each case study, different stress test levels were applied. The application to the selected CIs is presented following the workflow of ST@STREST, comprised of four phases: Pre-Assessment phase; Assessment phase; Decision phase; and Report phase. First the goals, the method, the time frame, and the appropriate stress test level to apply are defined. Then, the stress test is performed at component and system levels and the outcomes are checked and compared to the acceptance criteria. A stress test grade is assigned and the global outcome is determined by employing a grading system. Finally, critical events and risk mitigation strategies are formulated and reported to stakeholders and authorities.JRC.E.4-Safety and Security of Building