Ryuta Hataya

Dating of marine terrace sediments by ESR, TL and OSL methods and their applicabilities

Abstract We present the results of a pilot study in which ESR. TL and optical dating are intercompared to assess their suitabilities for application to measurement of the uplift rates of the Japanese Islands. Samples used were known-age marine ten-ace sediments collected from three sites in Central Japan. As a result of optical bleaching experiments, it was found that the TL residual intensity was identified by UV lamp, but we were not able to determine how the bleaching of the ESR Ti signal proceeded in antiquity. ESR, TL and optical dating were performed using the Ti signal. the red TL emission and the UV emissions measured during stimulation by the waveband 500±40 nm respectively. Equivalent doses were estimated using the additive-close method. Dose rates were calculated from radioisotope concentrations measured using neutron activation analysis. It was found that variation in pore water content over time was of major significance in age determinations for these sediments, on account of their history of deposition underwater, with subsequent uplift and drainage. It was concluded from the correspondence of ages estimated by TL and optical dating with geological expectation that the TL and optical dating methods are suitable for dating marine terrace sediments.

Estimation of pyrite oxidation rate by sulfate ion discharged from a catchment

Abstract The in situ rate of pyrite oxidation was estimated at a proposed dam site by measurements of the amount of SO 4 2− discharged from the site to evaluate the impact of the dam on the surrounding environment. The SO 4 2− concentrations and flows of streams were simultaneously measured. The results showed that the SO 4 2− concentration depended on the sampling location, and that the tributaries with high SO 4 2− concentration corresponded to the distribution of pyrite-bearing rocks. The total amount of SO 4 2− discharged at the site was calculated at approximately 7.5 Mg/km 2 /year, based on an integral of the product of the SO 4 2− concentration and stream flow with respect to time. The origins of the discharged SO 4 2− could be divided into two categories: 60% from pyrite-bearing rocks and 40% from wet deposits at the site. Therefore, the rate of the pyrite oxidation at the site was calculated to be approximately 2.8 Mg/km 2 /year. The total amounts of SO 4 2− discharged from the acid water-producing areas located upstream and downstream of the site were calculated as 13–27 Mg/km 2 /year. The resultant weathering rate was estimated as 0.03–0.28 mm/year by considering the dry density and the pyrite content of these areas.

Studies on a new ESR signal (R signal) of fault gouges for fault dating

Abstract A new ESR signal, designated R, is used for the ESR fault dating. The R signal is masked by the E′ signal at commonly used microwave powers, typically 1 mW, but is clearly distinguished from it at higher microwave powers. The R signal of quartz grains of the youngest fault gouge of the Atotsugawa fault, a major active fault in central Japan, was the most intense and increased remarkably by artificial gamma-ray irradiation, while source rocks have no R signal. It indicates that precursors of paramagnetic centres associated with the R signal are produced during or after faulting and that the R signal increases later. Our experiments reveal that heating prior to artificial irradiation is ineffective for the production of the precursors, and the precursors is made by another mechanism, probably mechanical fracturing at faulting. If so, the D E value by the R signal means the equivalent dose of natural radiation which a sample received after faulting. Therefore, the R signal might directly give the age of the most recent fault movement.

A new ESR signal (R signal) in quartz grains taken from fault gauges: its properties and significance for ESR fault dating

Abstract We have detected a new ESR signal, overlapping the E1′ signal, in quartz grains taken from thin gouge layers of active petrological faults. This newly observed signal (R signal) is better detected at high microwave powers. The intensity of the R signal increases by exposing to artificial gamma rays, whereas the E1′ signal intensity decreases. We consider that the equivalent dose for the R signal reflects the age of the most recent faulting, and that the equivalent doses for ‘the E1′ signal’ in the literature should be re-examined. Several properties of the R signal are presented along with t he equivalent dose for the R signal of quartz in fault gouges.

Chapter 6 The 1995 Kobe earthquake and problems of evaluation of active faults in Japan

Abstract The Kobe earthquake ( M 7.2) of January 17, 1995, which was the most damaging earthquake in recent Japanese history, made manifest the need for reconsidering the method of evaluating active faults. An earthquake of this magnitude at this time was unexpected according to conventional evaluation, in which the potential magnitude of earthquakes at a certain site is estimated by considering the greatest earthquake in the past 400 years and the length of the active fault. The following characteristics of this earthquake made it appear unlikely by conventional understanding: (1) the Kobe earthquake involved several neighboring faults, which had been previously been identified as separate fault systems: (2) the surface rupture of about 10 km length was much shorter than the 50 km seismic faulting; (3) the interval of 400 years between the Kobe and penultimate Keicho earthquake of 1596 AD ( M 7.5), which has been revealed by historical documents and some excavations, is much shorter than the 2000 years estimated by calculating the average slip rate of displaced landforms. These shortcomings imply that active fault evaluation with the traditional characteristic earthquake model which deals with each fault separately, is not adequate for an area like Japan where active faults swarm. New concepts such as the block rotation model ( Kanaori, 1990 ; Late Mesozoic-Cenozoic strike-slip and block rotation in the inner belt of Southwest Japan. Tectonophysics, 177: 381–399) considering the macroscopic tectonic framework for fault interactions are needed. Furthermore, fault dynamics cannot be ignored; physical and temporal parameters associated with faulting, such as moment release rate, must be considered for realistic and precise evaluation.