Tidal triggering of earthquakes in the subducting Philippine Sea plate beneath the locked zone of the plate interface in the Tokai region, Japan

We found a characteristic space–time pattern of the tidal triggering effect on earthquake occurrence in the subducting Philippine Sea plate beneath the locked zone of the plate interface in the Tokai region, central Japan, where a large interplate earthquake may be impending. We measured the correlation between the Earth tide and earthquake occurrence using microearthquakes that took place in the Philippine Sea plate for about two decades. For each event, we assigned the tidal phase angle at the origin time by theoretically calculating the tidal shear stress on the fault plane. Based on the distribution of the tidal phase angles, we statistically tested whether they concentrate near some particular angle or not by using Schuster's test. In this test, the result is evaluated by p-value, which represents the significance level to reject the null hypothesis that earthquakes occur randomly irrespective of the tidal phase angle. As a result of analysis, no correlation was found for the data set including all the earthquakes. However, we found a systematic pattern in the temporal variation of the tidal effect; the p-value significantly decreased preceding the occurrence of M ≥ 4.5 earthquakes, and it recovered a high level afterwards. We note that those M ≥ 4.5 earthquakes were considerably larger than the normal background seismicity in the study area. The frequency distribution of tidal phase angles in the pre-event period exhibited a peak at the phase angle where the tidal shear stress is at its maximum to accelerate the fault slip. This indicates that the observed small p-value is a physical consequence of the tidal effect. We also found a distinctive feature in the spatial distribution of p-values. The small p-values appeared just beneath the strongly coupled portion of the plate interface, as inferred from the seismicity rate change in the past few years.     

Crustal movement along a collision boundary of plates (case of eastern Taiwan)

Recent crustal movements in eastern Taiwan were investigated based on geodetic and seismological data as a case study of the tectonics along a colliding plate boundary. Secular horizontal strain along the Longitudinal Valley, a probable arc-continent collision boundary between the Philippine Sea and Eurasion plates, is compressive with a large rate of 2 microstrains/year, and the maximum compression axis trends in NW-SE direction. This means that nearly two-thirds of the convergence rate between the two plates is consumed in the narrow zone along the valley and confirms the view that the valley is the plate boundary between the two. The amount of uplift in the Central Range, deduced from trigonometric leveling, reaches more than one meter during the past 60 years. Such active orogeny is caused by the high strain rate in this area. Horizontal displacement of the Coastal Range, a leading edge of the Philippine Sea plate, has a left-lateral component, suggesting that the boundary is a region of oblique collision and the range moves toward the north, producing subduction of the Philippine Sea plate off the Coast of northeastern Taiwan.An extensional strain pattern is found northeastern Taiwan near Hualien, in northern Taiwan near Ilan, and in southeastern Taiwan south Taitung. In northeastern Taiwan, the direction of the maximum extension axis is nearly parallel to the isodipth contours of deep-focus earthquakes that occurred under the southern part of the Ryukyu Trench. From a model calculation using a finite-element method, this pattern of strain is interpreted as an edge effect of the collision-subduction junction in northeastern Taiwan. The direction of the maximum extension in northern Taiwan forms high angles with the direction of the tectonic line near Ilan stretching from the Okinawa Trough. This fact is harmonious with the view that the Okinawa Trough is spreading. Extensional strain observed in southeastern Taiwan may be related to the eastward subduction since the area is situated on a transition zone, from collision to subduction.     

Restoring forces on vertical circular cylinders forced by earthquakes

An eigenfunction solution is presented for the dynamic response of vertical circular cylinders to earthquake excitation in a compressible fluid of finite depth. This single eigenseries expansion eliminates the need for a double summation over both the eigenfunctions and the trial functions as required by Rayleigh-Ritz methods. Revised definitions for the added mass and hydrodynamic radiation damping coefficients per unit length are derived from the hydrodynamic fluid pressures. Based on comparisons between these newly defined coefficients, the compressibility of the fluid is found to be relatively more important at dimensionless frequencies greater than unity (ω > 1.0) when analysing both rigid and flexible cylinders having relatively large diameter to water depth ratios,r₀/h > 0.25 (squatty type). This conclusion regarding the relative importance of the fluid compressibility is derived from a comparison between the relative magnitudes and the vertical distributions over depth of both the added mass and radiation damping coefficients per unit length for both rigid and flexible squatty cylinders. From additional comparisons with Rayleigh-Ritz solutions that require trial functions, the results for totally immersed flexible slender cylinders (r₀/h< 0.10) are shown to be equivalent; but the results for totally immersed flexible squatty cylinders (r₀/h > 0.25) are not. The reason for this difference appears to be in the truncation of the trial function series in the Rayleigh-Ritz methods, which excludes the higher mode shapes, and in the definitions of the added mass coefficients. Comparisons with laboratory data for both rigid and flexible cylinders confirm the accuracy of the solutions obtained by the eigenseries in the limited frequency interval above the highest frequency for surface gravity waves (f > 1.0 Hz) and below the first dimensionless cut-off frequency for acoustic waves (ω< 1.0).     

Coupled Ce-Nd isotope systematics and rare earth elements differentiation of the moon

¹³⁸Ce/¹⁴²Ce and ¹⁴³Nd/¹⁴⁴Nd isotope ratios of lunar samples are determined to constrain the petrogenetic differentiation and evolution of the moon. High-precision Ce-Nd isotope data, well-defined Rb-Sr isochrons, and rare earth elements (REE) abundances of lunar samples show that unexpectedly low La/Ce ratios of evolved lunar highland samples are preserved from at least 3.9 Ga. Precise analysis of REE abundances indicates that the low La/Ce ratio results from a depletion of La relative to other REE. This depletion can be seen in pristine KREEP basalts and Mg-suite rocks from 3.85 to 4.46 Ga. As REE abundances of all these samples are controlled by the presence of a KREEP component, the depletion was probably inherited from a late crystallization sequence of the lunar magma ocean related to the production of the original KREEP component.     

Significance of stemflow in groundwater recharge. 2: A cylindrical infiltration model for evaluating the stemflow contribution to groundwater recharge

A primary model for evaluating the effect of stemflow on groundwater recharge has been developed. The model, a cylindrical infiltration model (CI model), is based on the infiltration area of stemflow-induced water instead of canopy projected area for determining the stemflow inputs to the soil surface. The estimated ratio of recharge rate by stemflow to the total recharge rate determined with this model agrees closely with values obtained from the mass balance of chloride in subsurface waters. This primary model is considered to be useful for estimating the effect of stemflow on groundwater recharge.     

Circulation patterns in the lower Arctic Ocean derived from geochemical data

Climatological water-mass structures were identified in the Arctic Ocean using the geochemical dataset in the Hydrochemical Atlas of the Arctic Ocean (HAAC) as well as data on a geochemically conserved parameter, PO₄*, based on phosphate and dissolved oxygen. In the upper ocean above a depth of 500 m, the HAAC was found to reliably depict the boundary between Pacific-Origin Water (P-Water) and Atlantic-Origin Water (A-Water), which is aligned 135°E–45°W near the surface but rotates counterclockwise with depth. Thus, the Arctic and Atlantic oceans exchange high-silicate P-Water and low-silicate A-Water. The PO₄* field in the lower ocean below a depth of 1500 m was analyzed statistically, and the results indicated that the Eurasian Basin receives low-PO₄* Nordic Seas Deep Water, which flows along the bottom from the Greenland Sea. The routes from the upper ocean to the lower ocean were determined. Only the southern portion of the Canada Basin, which receives water from the Chukchi and Beaufort Seas, has high PO₄* levels; the rest of the Amerasian Basin receives low-PO₄* water from the Laptev Sea and/or the Barents Sea. The Eurasian Basin receives moderate levels of PO₄* from the Fram Strait and from the intermediate layer. The intermediate-layer water gradually travels up from the lower ocean and returns to the Atlantic, entraining the subsurface portion. It is likely that high-PO₄* water occasionally flows down from the upper ocean along Greenland, making the Eurasian Basin heterogeneous.     

Estimating the provincial environmental Kuznets curve in China: a geographically weighted regression approach

This study estimates the environmental Kuznets curve (EKC) relationship at the province level in China. We apply empirical methods to test three industrial pollutants—SO₂ emission, wastewater discharge, and solid waste production—in 29 Chinese provinces in 1994–2010. We use the geographically weighted regression (GWR) approach, wherein the model can be fitted at each spatial location in the data, weighting all observations by a function of distance from the regression point. Hence, considering spatial heterogeneity, the EKC relationship can be analyzed region-specifically through this approach, rather than describing the average relationship over the entire area examined. We also investigate the spatial stratified heterogeneity to verify and compare risk factors that affect regional pollution with statistical models. This study finds that the GWR model, aimed at considering spatial heterogeneity, outperforms the OLS model; it is more effective at explaining the relationships between environmental performance and economic growth in China. The results indicate a significant variation in the existence of the EKC relationship. Such spatial patterns suggest province-specific policymaking to achieve balanced growth in those provinces.     

Eccentric installation of splice plates for compressive strength improvement of rectangular hollow section braces

Steel hollow section members are often applied as bracing in steel structures. Field-bolted connections of the slotted-in single splice plate and the gusset plate are popular because of their ease of construction. However, eccentricity between the splice and gusset plate axes reduces the compressive strength of the brace. This study proposes compressive strength improvement of rectangular hollow section braces using eccentrically installed splice plates such that the gusset plate axis coincides with the brace axis. To demonstrate the efficacy of the proposed concept, four compressive loading test results are examined in this study. Test results reveal the influences of splice plate eccentric installation on the brace compressive strength, the out-of-plane displacement, and the strain distribution. The proposed concept is effective for the brace with stiffened splice plates for inducing overall buckling with plastic hinges in the gusset plates. Variation of compressive strength is finally discussed based on the discrepancy between the brace axis and the axis of the plates in which the plastic hinges form at the overall buckling mode ends.     

Japan's earliest ostracods

Mesozoic, Cenozoic and especially Holocene ostracod faunas have been documented from Japan. Not surprisingly, considering the plate tectonic factors at play, very few ostracod faunas are known from its early Paleozoic successions. Our pilot studies have recovered new ostracod assemblages from early Paleozoic terranes of Japan. Acid preparation of carbonates has yielded low diversity, poorly preserved yet significant palaeocopid and podocopid ostracod faunas from Wenlock/Ludlow Series Silurian rocks at Gionyama in the Kurosegawa Terrane, Miyazaki Prefecture, Kyushu, and Hitoegane in the Hida‐Gaien Terrane, Gifu Prefecture, Honshu. The ostracod faunas include new eurychilinoid (Pauproles supparata gen. et sp. nov.), hollinoid (Hollinella orienta sp. nov.) and beyrichioid (Clintiella antifrigga sp. nov.) palaeocopid taxa. Conodonts recovered from the same sample as the ostracods from Gionyama confirm a mid‐Silurian age for the part of the Gionyama Formation in question. The ostracod faunas recovered from Gionyama and Hitoegane are the first confirmed, well‐documented record of the group from the Silurian of Japan and are therefore the earliest known ostracods from that country (a previous record of purported Ordovician ostracods from Japan is incorrect). The ostracod taxa display links with the paleocontinents of particularly Laurentia and Baltica and demonstrate a pan‐tropical signature; it appears that climate control was stronger than geographical control in shaping this pattern of ostracod distribution. The material recovered includes adult dimorphic (assumed sexual) pairs of three palaeocopid species, which represent Japan's oldest (423–433 million years) known ‘couples’.