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Abstract: Increasing vulnerability of metropolitan areas to earthquake and the very low probability level at which short term earthquake forecasting is possible make earthquake early warning methods (EEW) the main viable alternative for effective risk reduction in cities. Preventive actions, such as retrofitting and building and the diffusion of construction codes, are of course essential. They are not sufficient. A substantial proportion of the population in areas of higher earthquake hazard still reside in buildings that do not meet modern earthquake resistant standards, and cannot currently be strengthened in an economically viable manner. As demonstrated in Japan EEW has the potential of significantly contributing to reduce individual vulnerability of urban population to earthquakes. Future research on EEW should be focused on its implementation to protect lifelines, infrastructures and strategic buildings, and it should include training of administrators and people who can fully exploit the technological advantages offered by EEW systems. In particular it should foresee extensive cost-benefit analysis for each potential application, the identification and solution of legal problems (such as liability in the event of false or missed alarms), education and training, both for mitigation and response, as well as detection and processing within 1s of the first seismic wave arrivals. Further objectives include the development of people-centred EEW, specialized IT and decision making support systems, integration of sensors, communications and decision making systems, integration into programs of eco-sustainable development, and integration with other EW systems (all hazard systems). [ABSTRACT FROM AUTHOR]

Abstract: Magma is fed to a volcano through a complex “plumbing” system that involves not only shallow structures beneath the volcano edifice, but also deep structures and processes within the underlying crust and upper mantle. This paper summarizes seismic experiments carried out over many years at Gunung Merapi in Central Java. These have resolved the 3D seismic velocity structure of the Merapi edifice, and provided a 3D structural image of the lithosphere and subduction zone beneath Central Java. Earthquake locations reveal that with distance from the trench, the dip of the subducting slab steepens from nearly horizontal (0–150km), through 45° (150–250km), to 70° (>250km). The slab appears as a 30km thick double layer of seismicity in a depth range of 80km to 150km, and it can be identified seismically to a depth of more than 600km. The active volcanoes of Merapi, Sumbing, and Lawu are located at the edge of a large low velocity body that extends from the upper crust to the upper mantle beneath Central Java. Shear wave signals recorded above this anomaly are strongly attenuated compared to neighboring areas. The anomalous body has a detected volume of >50,000km3 and a decrease in P and S velocities relative to adjacent regions of up to 30%. The resulting Vp/Vs ratio of up to 1.9 is unusually high for lower crust. Additionally, the anomaly extends along a 45 degree-slope downward from beneath the volcanic arc and meets the slab at 100km depth. We interpret this sloping anomaly as a pathway for fluids and partial melts. Increased seismicity is observed at depths of ~100km, possibly as a result of dehydration of the subducting slab with related fluid releases causing partial melting of overlying mantle material. The large velocity reduction and high Vp/Vs ratio in the region are consistent with an increase in temperature, a reduction of shear strength, and the presence of fluids or melts of 13 to 25vol.%. The detected strong anomaly beneath Central Java is unique in size and amplitude compared to other subduction zones. The geophysical evidence suggests that this segment of the arc has a high magma flux and is thus capable of developing even larger shallow crustal reservoirs and more voluminous explosive eruptions in the future. [Copyright &y& Elsevier]

Abstract: Characterizing the local site response in large cities is an important step towards seismic hazard assessment. To this regard, single station seismic noise measurements were carried out at 146 sites in the northern part of Santiago de Chile. This extensive survey allowed the fundamental resonance frequency of the sedimentary cover, derived from horizontal-to-vertical (H/V) spectral ratios, to be mapped. By inverting the spectral ratios under the constraint of the thickness of the sedimentary cover, known from previous gravimetric measurements, local S-wave velocity profiles have been retrieved. After interpolation between the individual profiles, the resulting high resolution 3D S-wave velocity model allows the entire area, as well as deeper parts of the basin, to be represented in great detail. Since one lithology shows a great scatter in the velocity values only a very general correlation between S-wave velocity in the uppermost 30m () and local geology is found. Local S-wave velocity profiles can serve as a key factor in seismic hazard assessment, since they allow an estimate of the amplification potential of the sedimentary cover. Mapping the intensity distribution of the 27 February 2010 Maule, Chile, event (Mw =8.8) the results indicate that local amplification of the ground motion might partially explain the damage distribution and encourage the use of the low cost seismic noise techniques for the study of seismic site effects. [Copyright &y& Elsevier]

Abstract: Single station seismic noise measurements were carried out at 192 sites in the western part of Istanbul, Turkey. This extensive survey allowed the fundamental resonance frequency of the sedimentary cover to be mapped, and identify areas prone to site amplification. The results are in good agreement with the geological distribution of sedimentary units, indicating a progressive decrease of the fundamental resonance frequencies from the northeastern part, where the bedrock outcrops, towards the southwestern side, where a thickness of some hundreds meters for the sedimentary cover is estimated. The particular distribution of fundamental resonance frequencies indicates that local amplification of the ground motion might play a significative role in explaining the anomalous damage distribution after the 17 August 1999 Kocaeli Earthquake. Furthermore, 2D array measurements of seismic noise were performed in the metropolitan area with the aim of obtaining a preliminary geophysical characterization of the different sedimentary covers. These measurements allow the estimation of the shear-wave velocity profile for some representative areas and the identification of the presence of strong impedance contrast responsible of seismic ground motion amplification. Comparison of a theoretical site response from an estimated S-wave velocity profile with an empirical one based on earthquake recordings strongly encourages the use of the low cost seismic noise techniques for the study of seismic site effects. [Copyright &y& Elsevier]