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Groundwater is a necessary and indispensable resource in the gradual depletion of the amount in the world. Groundwater storage is an important indicator to evaluate the capability of volume of water can be released from the aquifer. This research highlights a new assessment to infer the storage of aquifer using earthquakes activated around East Asia and the ring of fire at West Pacific Ocean. Ten significant seismic events are used to evaluate the groundwater storage at an observation station. By analyzing the spectra of groundwater level and seismogram, it is evident that the period varied in 7–25 s of Rayleigh waves significantly dominate propagation from the epicenter of earthquakes to the observation station. The storage coefficient is then shown in the order of 10 −4 –10 −3 . The major innovation of this study suggests that to concretely deduce the groundwater storage by earthquake activity has become feasible. [ABSTRACT FROM AUTHOR]

SUMMARY We present models of the 3-D shear velocity structure of the lithosphere and asthenosphere beneath the Hawaiian hotspot and surrounding region. The models are derived from long-period Rayleigh-wave phase velocities that were obtained from the analysis of seismic recordings collected during two year-long deployments for the Hawaiian Plume-Lithosphere Undersea Mantle Experiment. For this experiment, broad-band seismic sensors were deployed at nearly 70 seafloor sites as well as 10 sites on the Hawaiian Islands. Our seismic images result from a two-step inversion of path-averaged dispersion curves using the two-station method. The images reveal an asymmetry in shear velocity structure with respect to the island chain, most notably in the lower lithosphere at depths of 60 km and greater, and in the asthenosphere. An elongated, 100-km-wide and 300-km-long low-velocity anomaly reaches to depths of at least 140 km. At depths of 60 km and shallower, the lowest velocities are found near the northern end of the island of Hawaii. No major velocity anomalies are found to the south or southeast of Hawaii, at any depth. The low-velocity anomaly in the asthenosphere is consistent with an excess temperature of 200-250 °C and partial melt at the level of a few percent by volume, if we assume that compositional variations as a result of melt extraction play a minor role. We also image small-scale low-velocity anomalies within the lithosphere that may be associated with the volcanic fields surrounding the Hawaiian Islands. [ABSTRACT FROM AUTHOR]

Abstract: Direct seismic measurements of the thickening of oceanic lithosphere away from the spreading axis are rare due to the remoteness of mid ocean ridges. On the East Pacific Rise, at 17°S, there were two long-term broadband ocean bottom seismometer deployments, the MELT and GLIMPSE experiments. These arrays spanned young Pacific plate seafloor ranging in age from 0 to 8 Ma. Combining these two data sets, we describe the increase in Rayleigh wave phase velocities for 16–100 s period as function of distance from the ridge with two parameterizations: an arbitrary function of seafloor age and a simple polynomial function of age on the Pacific and Nazca plates. Although resolution analysis shows that 10 to 15 independent pieces of information about the age variation of phase velocity on the Pacific plate can be resolved at periods of ≤50 s, the three parameter polynomial model fits the data almost as well, indicating a simple pattern of the evolution of structure with age. To compare our observations to the predictions for the conductive cooling of the lithosphere, we convert a thermal half-space cooling model to shear velocity using anharmonic and anelastic contributions. The patterns in the velocities are not consistent with simple conductive cooling. The conductive cooling model under predicts the changes in phase velocity with age observed in the 20 to 78 s period range. We observe significant changes in shear velocity in the asthenosphere at depths greater than conductive cooling should extend. The asthenospheric low velocity zone is asymmetric, dipping to the west with the lowest velocities beneath the Pacific plate west of the spreading center. The conductive cooling model also over predicts the shear velocities in the lithosphere by ~0.2 km/s. These anomalies indicate that more complicated mantle flow and significant mantle heterogeneities such as melt are required. [Copyright &y& Elsevier]

We present a regional surface waveform tomography of the Pacific upper mantle, obtained using an automated multimode surface waveform inversion technique on fundamental and higher mode Rayleigh waves, to constrain the structure down to ∼400 km depth. We have improved on previous implementations of this technique by robustly accounting for the effects of uncertainties in earthquake source parameters in the tomographic inversion. We have furthermore improved path coverage in the South Pacific region by including Rayleigh wave observations from the French Polynesian Pacific Lithosphere and Upper Mantle Experiment deployment. This improvement has led to imaging of vertical low-velocity structures associated with hotspots within the South Pacific Super-Swell region. We have produced an age-dependent average cross-section for the Pacific Ocean lithosphere and found that the increase in with age is broadly compatible with a half-space cooling model of oceanic lithosphere formation. We cannot confirm evidence for a Pacific-wide reheating event. Our synthetic tests show that detailed interpretation of average trends across the Pacific Ocean may be misleading unless lateral resolution and amplitude recovery are uniform across the region, a condition that is difficult to achieve in such a large oceanic basin with current seismic stations. [ABSTRACT FROM AUTHOR]

The fundamental mode Rayleigh, R2, and R3 waves were used to study the phase velocity tomography and surface-wave attenuation variation beneath the Pacific Ocean. The Rayleigh-wave phase velocity estimation for about 4000 propagation paths across the Pacific Ocean were made at time periods of 70, 100, 150, and 230 sec. More than 100 earthquakes, which occurred in the Pacific Ocean and were recorded at about 60 broadband digital seismic networks ascribed to IRIS, OHP, TERRAscope, Pacific 21 (formerly POSEIDON), and the Pacific Northwest Region (UW), are used in this study. The resulting phase velocity maps at varying periods showed a good correlation with known geological and tectonic features of the region. A fast-velocity anomaly is surrounded by a slow-velocity anomaly over the eastern and western parts of the Pacific Ocean, while the central part is associated with a fast-velocity anomaly. Subduction zones and spreading regions are demarcated by slow-velocity anomalies. A slow-velocity anomaly is also clearly visible over the Hawaiian hot spots and the French Polynesia, Micronesia, Japan, and Java-Sumatra trench axis zones. A high-attenuation zone (low Q-value) is visible over the East Pacific rise and Nazca plate and Cocos plate regions of younger lithospheric age, and a low-attenuation anomaly (high Q-value) marks the zones of older lithosphere in the western part of the Pacific Ocean. High-attenuation regions are surrounded by low-attenuation zones in the eastern and western Pacific Ocean. Subduction zones with lower attenuation are flanked by high-attenuation anomalies on both sides, reflecting the plate interaction. The hot spots are associated with a high-attenuation zone of the Pacific Ocean at a depth of 100-300 km. [ABSTRACT FROM AUTHOR]

The fundamental mode Rayleigh wave generated by 27 earthquakes and recorded at 11 digital broadband seismic stations belonging to the Ocean Hemisphere Project network in the northwest Pacific region are analyzed to estimate the Rayleigh-wave group velocity for 160 paths at periods from 10 to 50 sec. The inverted group velocity results suggest a quasi-continental oceanic transitional structure of the northwest Pacific Ocean with 21 km as an average crustal thickness. The Rayleigh-wave group velocity tomography results for short time periods (10-50 sec) showed a good correlation with known geological and tectonic features and were consistent with the tectonic complexities of the region. Slow-velocity anomalies at varying periods correspond to ridges, basins, trenches, and volcanic fronts of the northwest Pacific Ocean while the fast-velocity anomalies show the effects of plate interactions at relatively longer periods (30-50 sec). A triple junction formed by the subduction of the Phillipine Sea and Pacific plates beneath the Eurasian plate is imaged by a high-velocity zone in this study. [ABSTRACT FROM AUTHOR]

We obtained phase velocities of fundamental Rayleigh waves in the northwestern Pacific ocean and the northern Philippine sea from seismograms retrieved from a long-term broad-band ocean bottom seismometer (LT-OBS) array deployed in 1999–2000 and from those recorded in Japan, Guam and Ponape islands. This array observation was one of the first attempts to record continuous seismograms on the seafloor using broad-band seismographs on a long-term basis. The geographical distribution of the LT-OBS stations and the surrounding land stations enabled us to determine pure-path phase velocities in a frequency range from 0.01 to 0.05 Hz across the Mariana trough, the Parece Vela basin, the Shikoku basin and the Minami Daito basin, which were found to be systematically lower than those of the Pacific seafloor at comparable ages. This result, along with other geophysical and geological observations in the Philippine sea, may be explained by an uppermost mantle that is relatively Fe rich. [ABSTRACT FROM AUTHOR]