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

Seismic analysis of motorway bridges accounting for key structural components and nonlinear soil-structure interaction

The paper introduces an efficient methodology to analyze the seismic performance of motorway bridges. Rigorous 3D models of a typical overpass bridge are developed and used to assess the efficiency of the proposed method. Fixed-base conditions are initially considered to focus on the effect of key structural components. The proposed simplified model is composed of a SDOF system of a pier with lateral and rotational springs and dashpots connected at the top, representing the deck and the abutment bearings. Its definition requires section analysis of the pier, and computation of spring and dashpot coefficients using simple formulas. It is shown that the lateral and rotational restraint provided by the deck and the abutment bearings is not at all negligible and should be taken into account. The simplified model is extended to account for nonlinear soil-structure interaction, replacing the soil-foundation system with horizontal, vertical, and rotational springs and dashpots. While the horizontal and vertical springs and dashpots are assumed elastic, the nonlinear rotational spring is defined on the basis of non-dimensional moment-rotation relations. The simplified model compares well with the full 3D model of the bridge-abutment-foundation-soil system, and is therefore considered a reasonable approximation.</p

Extending displacement-based earthquake loss assessment (DBELA) for the computation of fragility curves

This paper presents a new procedure to derive fragility functions for populations of buildings that relies on the displacement-based earthquake loss assessment (DBELA) methodology. In the method proposed herein, thousands of synthetic buildings have been produced considering the probabilistic distribution describing the variability in geometrical and material properties. Then, their nonlinear capacity has been estimated using the DBELA method and their response against a large set of ground motion records has been estimated. Global limit states are used to estimate the distribution of buildings in each damage state for different levels of ground motion, and a regression algorithm is applied to derive fragility functions for each limit state. The proposed methodology is demonstrated for the case of ductile and non-ductile Turkish reinforced concrete frames with masonry infills

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

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

Simple method for real-time seismic damage assessment of bridges

Seismic damage of bridges may pose a severe threat to motorway users, and preventive closure until post-seismic inspection may be viewed as the only safe option. However, such a measure may incur pronounced losses by obstructing transportation of rescue teams. On the other hand, allowing traffic on earthquake-damaged bridges is a difficult decision with potentially dire consequences. Hence, the main dilemma for the motorway administrator is whether to interrupt the operation of the network, calling for timely development and implementation of a RApid REsponse (RARE) system. The development of such a RARE system requires an effective means to estimate the seismic damage of motorway structures in real time. This paper contributes towards such a direction by introducing a simple method for real time seismic damage assessment of motorway bridges. The proposed method requires nonlinear dynamic time history analyses using multiple seismic records as seismic excitation. Based on the results of the analyses, statistical models are estimated, and nonlinear regression equations are developed to express seismic damage as a function of statistically significant intensity measures (IMs). Such equations are easily programmable and can be employed for real-time damage assessment, as part of an online expert system. In the event of an earthquake, the nearest seismic motion(s), recorded by an online accelerograph network, will be used in real time to estimate the damage state of motorway structures, employing the developed equations. The efficiency of the proposed method is demonstrated using a single bridge pier as an illustrative example. Based on finite element (FE) analysis results, three nonlinear regression models are estimated correlating three damage indices (DIs) with statistically significantly IMs.</p

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

Dynamic Properties of Embankment Dams

Forced vibration test result are presented for two large embankment dams. The results are compared with an approximately three dimensional finite element analysis. In addition a semi-empirical fundamental period expression is developed for use in the interpretation of the available natural period data. The period expression developed is based on the shear wedge solution for an inhomogeneous medium and takes the effect of the third dimension into account