Detection of possible seismic station phase reversals using parametric data from seismological bulletins

<p>A simple and fast technique to detect systematic changes in the performance of seismic stations by using parametric data is being presented. The methodology is based on a simple principal, notably, quantifying the goodness of fit of first motion manually picked polarities from seismological bulletins versus available earthquake mechanism solutions over time. The probability of the reporting polarity data fitting (and not fitting) source mechanisms is quantified by calculating the probability distribution of several Bernoulli trials over a randomly perturbed set of hypocentres and velocity models for each earthquake mechanism - station polarity combination. The method was applied to the registered seismic stations in the bulletin of the International Seismological Centre (ISC) after grouping each polarity pick by reporting agency, using data from the past two decades. The overall agreement of first motion polarities against source mechanisms is found to be good with a few cases of seismic stations showing indications of systematic phase reversals over certain time periods. Specifically, results were obtained for 50% of the registered stations at the ISC, and from these stations 70% show reliable operation during the operational time period under investigation, with only 3% showing the opposite, and 7% showing evidence of systematic changes in the quality of the reported first motion polarities. The rest showed great variability over short periods of time, which does not allow one to draw any conclusions. Comparing waveform data with the associated reported polarities revealed a mixture of cases of either questionable picking or true station phase reversals.</p>

An analytical model of multi-stress drops triggered by localized microcrack damage in brittle rocks during progressive failure

Stress drops in stress–strain constitutive curves of intact brittle rocks under high confining pressure have great significance for evaluating the earthquake mechanism and the safety of deep underground engineering. Microcrack growth in intact rock strongly influences the stress drops. However, the theoretical model of microcrack growth-dependent multi-stress drops rarely is proposed in stress–strain curves of intact rocks. In this study, a constitutive model depending on the damage variable relating to microcrack growth and strain increment is proposed to explain the multi-stress drops in stress–strain curves including strain hardening and softening phases of intact rocks. This model is formulated by combining the wing crack growth model, the suggested relationship between axial strain and wing crack growth, and the stepping function of damage relating to axial strain. This stepping function of damage relating to axial strain approximately is used to simulate the developing process of the small individual shear bands caused by the local microcrack accumulation and coalescence. The effects of parameters in the suggested stepping function of damage on the stress–strain curves containing stress drops are discussed. The theoretical model qualitatively explains the experimental phenomena of multi-stress drops in the stress–strain curves, which provides an important implication for evaluating the earthquake mechanism and the safety of deep underground engineering.

Urgency Evaluation of the Nankai Great Earthquake and Tsunami by Scientific Ocean Drilling

Drilling can help researchers to garner a better understanding of earthquakes. The way to do this is to drill at least 5km below the sea floor. Rock samples can be gathered and tested, which can provide answers to a whole host of unknowns. This work can lead to important breakthroughs that enable scientists to better understand the earthquake mechanism, and enables a better forecasting seismic hazards across the globe. Masa Kinoshita is part of a highly collaborative team 'NanTroSEIZE' under the International Ocean Discovery Program (IODP), comprising more than 200 researchers from different countries. He is working on a Japan Society for the Promotion of Science-funded project entitled 'Urgency Evaluation of the Nankai Great Earthquake and Tsunami by Scientific Ocean Drilling' (lead by Gaku Kimura) that is seeking to estimate the earthquake likelihood of a severe Nankai Trough earthquake. Experts predict that there is a 70 to 80 per cent possibility that a so-called 'Nankai Trough megaquake' with a magnitude of 8 to 9 will occur in the next 30 years. The goal of the project is to establish better understanding of the state and properties of the Nankai seismogenic zone, and better assess the urgency of the predicted megaquake.

Earth Quake Model 2.0 : Attract Force Equation Release Earthquake Mechanism with Explaining Related Phenomena

Earth quake was nature phenomena, which has huge destroyed power, and make huge economic loss and human injuries and deaths. The reason of Earth quake has caused lots of researches. And predicting Earthquake has been the very important work on every day. While the mechanism of Earth quake was still unclearly, and the Earthquake predictions were still at initial stage. This paper use attract force mathematic physics model to build Earthquake mechanism model by finite element method, and try to explain the reason of Earthquake formation. At same time it was used to explain the related phenomena about Earthquake. The aims were to help for accurate predict Earthquake, and try to redeem the economic loss and save more people. This model was named Earth Quake Model 2.0, which was different and distinguished from the models before, and it was wish to help for seismic researches.