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Earthquake magnitude distributions among faults within a fault system are determined from regional seismicity and fault slip rates using binary integer programming. A synthetic earthquake catalog (i.e., list of randomly sampled magnitudes) that spans millennia is first formed, assuming that regional seismicity follows a Gutenberg-Richter relation. Each earthquake in the synthetic catalog can occur on any fault and at any location. The objective is to minimize misfits in the target slip rate for each fault, where slip for each earthquake is scaled from its magnitude. The decision vector consists of binary variables indicating which locations are optimal among all possibilities. Uncertainty estimates in fault slip rates provide explicit upper and lower bounding constraints to the problem. An implicit constraint is that an earthquake can only be located on a fault if it is long enough to contain that earthquake. A general mixed-integer programming solver, consisting of a number of different algorithms, is used to determine the optimal decision vector. A case study is presented for the State of California, where a 4 kyr synthetic earthquake catalog is created and faults with slip ≥3 mm/yr are considered, resulting in > 10 6 variables. The optimal magnitude distributions for each of the faults in the system span a rich diversity of shapes, ranging from characteristic to power-law distributions. [ABSTRACT FROM AUTHOR]

Multiple geophysical parameters including groundwater level, water temperature, water radon, crustal deformation, electromagnetic waves and total electron contents (TEC) in the ionosphere, are examined together to investigate pre-earthquake anomalous phenomena associated with the Mw6.1 Ludian earthquake on August 3, 2014. Cross-parameter comparison eliminates anomalies that are detected in one parameter only and examine earthquake-related phenomena in various fields, simultaneously. Retrieved anomalies show that abnormal decreases of water temperature and radon concentration related to anomalous uplift of groundwater levels appeared about 1–8 days before the earthquake even without contributions from rain. Significant step-like changes are observed from data recorded by strainmeters on July 31 and are consistent with water-related anomalies in timing. No significant anomalies can be found from electromagnetic data through the preliminary observation. In contrast, TEC appeared positive anomalies 1–3 days before the Ludian earthquake. Although causal mechanisms of the TEC anomalies from stressed rocks are not fully understood, multiple-parameter examination can increase credibility of determination regarding pre-earthquake phenomena. [ABSTRACT FROM AUTHOR]

This study examines the relationships between seismo-deformation and seismo-conductivity anomalies during two M6 earthquakes that occurred on March 27th and June 2nd, 2013 in Taiwan. The Hilbert–Huang Transform is applied on surface displacement data to remove the effects of noise, semi-annual and annual cycles, and the long-term plate movements. The residual displacements have similar orientations when earthquake-related stress accumulates in the crust. Once the accumulated stress approaches the threshold for fault rupture, the orientations of the residual displacements generally become random, except in a small region near the epicenter. Interestingly, high-conductivity anomalies, which can be detected from the 3-component magnetic data via the magnetic transfer function, exist in places very close to this small region near the epicenter. Spatial and temporal correlations between the high-conductivity anomalies and the small region of seismo-deformation anomalies suggest that electric charges may migrate and become trapped in the region during seismogenic processes due to differential stress accumulation. These electric charges form a high-conductivity material that affects the Parkinson vector of the geomagnetic field. [ABSTRACT FROM AUTHOR]

Abstract: The pressure and temperature evolution of an intense dielectric relaxation mechanism in as-received and wetted limestone (from Ioannina region (Greece)) are studied experimentally through complex impedance spectroscopy. The relaxation time decreases on compression, yielding a negative value for the corresponding activation volume. Furthermore, the role of water incorporated in the mineral was examined, revealing the remarkable fact that water not only enhances the absolute value of negative derivative of Gibbs energy with respect to pressure but also lowers significantly the energy barrier of the corresponding physical processes. Both findings are crucial for the explanation of the sensitivity of an electrotelluric station at Ioannina region in detecting Seismic Electric Signals emitted prior to earthquakes. [Copyright &y& Elsevier]

Abstract: An automatic analysis code called ANISOMAT+ has been developed and improved to automatically retrieve the crustal anisotropic parameters fast polarization direction (ϕ) and delay time (δt) related to the shear wave splitting phenomena affecting seismic S-wave. The code is composed of a set of MatLab scripts and functions able to evaluate the anisotropic parameters from the three-component seismic recordings of local earthquakes using the cross-correlation method. Because the aim of the code is to achieve a fully automatic evaluation of anisotropic parameters, during the development of the code we focus our attention to devise several automatic checks intended to guarantee the quality and the stability of the results obtained. The basic idea behind the development of this automatic code is to build a tool able to work on a huge amount of data in a short time, obtaining stable results and minimizing the errors due to the subjectivity. These behaviors, coupled to a three component digital seismic network and a monitoring system that performs automatic pickings and locations, are required to develop a real-time monitoring of the anisotropic parameters. [Copyright &y& Elsevier]

Abstract: Transient electric signals emitted prior to earthquake occurrence are recorded at certain sites in the Earth''s crust termed sensitive. These field observations enforce the laboratory investigation of the dielectric response of rocks forming these localities. The dielectric relaxation of granodiorite rock coming from such a sensitive locality (Keratea, Greece) reveals, through complex impedance spectroscopy, that the activation volume for relaxation of this rock is negative that so far has been reported only rarely. This result, however, supports a theoretical model on the pre-seismic electric signals and is likely to be correlated with the sensitivity of the site and hence with the selectivity. [Copyright &y& Elsevier]

Abstract: Many researchers studied the relationships between appearances of geomagnetic anomalies and their distances to earthquake epicenters or faults. Yet, occasionally some magnetometer stations located nearby earthquake epicenters and/or faults do not observe geomagnetic anomalies. In this paper, a new hybrid system which simultaneously takes the hypocenter and fault plane solution into account is constructed to examine 38 earthquakes interpreted to be associated with geomagnetic anomalies during the period 1988–2001 in Taiwan. The Surface Magnetic Anomaly Reference Tip (SMART) of the new system is used instead of the epicenter or the fault to investigate statistically the distance relationship between the anomalies and the earthquake parameters. Results show that the anomalies gather along the fault and in the belt zone to the SMART. Possible mechanisms causing the anomalies in the two zones are proposed and discussed. Characteristics of the anomaly might shed some light on locations of faults before earthquake occurrences. [Copyright &y& Elsevier]

Abstract: The aim of this paper is to characterize the spatio-temporal distribution of Central-Europe seismicity. Specifically, by using a non-parametric statistical approach, the proportional hazard model, leading to an empirical estimation of the hazard function, we provide some constrains on the time behavior of earthquake generation mechanisms. The results indicate that the most conspicuous characteristics of M W 4.0+ earthquakes is a temporal clustering lasting a couple of years. This suggests that the probability of occurrence increases immediately after a previous event. After a few years, the process becomes almost time independent. Furthermore, we investigate the cluster properties of the seismicity of Central-Europe, by comparing the obtained result with the one of synthetic catalogs generated by the epidemic type aftershock sequences (ETAS) model, which previously have been successfully applied for short term clustering. Our results indicate that the ETAS is not well suited to describe the seismicity as a whole, while it is able to capture the features of the short- term behaviour. Remarkably, similar results have been previously found for Italy using a higher magnitude threshold. [Copyright &y& Elsevier]

Abstract: Negative defect activation volumes are extremely rare in solids. Here, we report for the first time that this holds in a couple of hydrated rocks for dielectric relaxation by exploring the complex impedance spectra at various pressures and temperatures. The present findings mean that the relaxation time of the relevant relaxation mechanisms decreases upon increasing pressure, thus it may become too short at higher pressure and hence lead to the emission of transient electric signals before fracture. This may constitute the long-standing laboratory confirmation for the explanation of the generation of electric signals prior to an earthquake, as recently pointed out by Uyeda et al. [Tectonophysics 470 (2009) 205–213]. [Copyright &y& Elsevier]