A Comparison of Methods of Estimating the Attenuation of Earthquake Strong Ground Motion

Strong ground-motion attenuation relations take on a variety of forms, depending upon the parameters used to express the relations and upon the geographic area for which the equations are developed. In general the strong ground-motion parameters, namely acceleration, velocity, displacement and response spectra ordinates, are taken to be proportional to the distance from the earthquake source to the site, to the magnitude or some measure of the strength of the earthquake source, and to loss factors resulting from transmission of energy through the inelastic earth. In certain areas of the world, where strong-motion data are abundant, empirical relations can be developed to express these relations. In other areas of the world, where strong-motion data are few or are entirely lacking, more attention must be given to theoretical considerations. In this paper we give case histories of two such types of regions, namely western North America with an abundance of data and eastern North America with a paucity of data

The tailings dam failure of 5 November 2015 in SE Brazil and its preceding seismic sequence

The collapse of a mine tailings dam and subsequent flood in SE Brazil on 5 November 2015 was preceded by a small-magnitude seismic sequence. In this report, we explore the spatiotemporal associations between the seismic events and the accident and discuss their possible connection. We also analyze the signals generated by the turbulent mudflow, as recorded by the Brazilian Seismographic Network (RSBR). In light of our observations, we propose as possible contributing factor for the dam collapse either ground shaking and/or soil liquefaction triggered by the earthquakes. The possibility of such a small-magnitude earthquake contributing to the collapse of a tailings dam raises important concerns regarding safety and related legislation of dams in Brazil and the world. ©2016. American Geophysical Union.H.A.D. and M.A. acknowledge support from Sao Paulo Research Foundation FAPESP grant 2014/09455-3 and CNPq grant 30.6547/2013-9.Peer reviewe

A New Paradigm for Large Earthquakes in Stable Continental Plate Interiors

Large earthquakes within stable continental regions (SCR) show that significant amounts of elastic strain can be released on geological structures far from plate boundary faults, where the vast majority of the Earth's seismic activity takes place. SCR earthquakes show spatial and temporal patterns that differ from those at plate boundaries and occur in regions where tectonic loading rates are negligible. However, in the absence of a more appropriate model, they are traditionally viewed as analogous to their plate boundary counterparts, occuring when the accrual of tectonic stress localized at long-lived active faults reaches failure threshold. Here we argue that SCR earthquakes are better explained by transient perturbations of local stress or fault strength that release elastic energy from a pre-stressed lithosphere. As a result, SCR earthquakes can occur in regions with no previous seismicity and no surface evidence for strain accumulation. They need not repeat, since the tectonic loading rate is close to zero. Therefore, concepts of recurrence time or fault slip rate do not apply. As a consequence, seismic hazard in SCRs is likely more spatially distributed than indicated by paleoearthquakes, current seismicity, or geodetic strain rates