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Summary: It was found that groundwater can be fluctuated by a variety of disturbances. For instance, seismic activity inducing the dilatation of earth can disturb groundwater level fluctuation as observed in groundwater wells. In this research, spectral analysis in the frequency domain was used to quantitatively evaluate coherence between groundwater head fluctuations and the ground motions recorded in Taiwan from a distant earthquake, the 2011 Tohoku earthquake in northern Honshu, Japan with magnitude of 9. The relationship between groundwater fluctuations and the decomposed ground motions of Rayleigh waves are clearly identified. By analyzing autospectral density, cross-spectral density, and resultant coherence for the seismograms and groundwater head, it was found that the Rayleigh waves dominated the groundwater fluctuations at period of about 21–32s for six pair of groundwater and seismograms of broadband distributed around Taiwan; fluctuations of groundwater are highly coherent with the radial and vertical components of ground motions. Our analysis also shows the time from event to station for Rayleigh waves ranged from 780 to 900s approximately. Wave parameter for seismic event to station of groundwater and seismograms were also identified as 3.0–3.5km/s and 64–110km for wave velocity and wave length, respectively. The relationship of groundwater fluctuations and ground motions induced by seismic activity become feasible to assess using spectral analysis. [Copyright &y& Elsevier]

Abstract: Modern technology allows real-time seismic monitoring facilities to evolve into earthquake early warning (EEW) systems, capable of reducing deaths, injuries, and economic losses, as well as of speeding up rescue response and damage recovery. The objective of an EEW system is to estimate in a fast and reliable way the earthquake’s damage potential, before the strong shaking hits a given target. The necessary framework for EEW implementation is provided by the observed relationships between different parameters measured on the signal onsets and the final earthquake size. The implication of these observations on the physics of fracture processes has given rise to a significant debate in the seismological community. Currently, EEW systems are implemented or under testing in many countries of the world, and different methodologies and procedures have been studied and developed. The leading experience of countries like Japan or Mexico shows that, with a proper education of population and end-users, and with the design of real-time systems for the reduction of vulnerability/exposure, EEW can be an effective approach to the mitigation of the seismic risk at short time-scales. [ABSTRACT FROM AUTHOR]

A transition and subduction zone adjacent to the Ryukyu Arc, Ryukyu Trench, and Okinawa Trough, extends between southern Japan and northeastern Taiwan. It is generated during the northwestward subduction of the Philippine Sea Plate, which lies the Eurasian Plate along the Ryukyu Trench. The movement of the Philippine Sea Plate is hindered at the northeastern corner of Taiwan, which causes complicated structure of the Philippine Sea Plate at the western end of the Ryukyu subduction zone. Development of the active subduction and transition boundary near the western Ryukyu Arc is evaluated statistically by using displacements derived from GPS site data. The statistical model shows that the absolute displacement derived from GPS measurements of nearly 8 years indicates a maximum spatial variation of 0.625 m. Three trends are observed for such long-term progress, and use of linear regression also reveals quite good consistency between the data and statistic models. Such rate is also elevated following the trend development. Southeastern and nearly horizontal movement is suggested to the main development of for the site movements, it is likely related to the tensional activity adjacent to this boundary. [ABSTRACT FROM AUTHOR]