252 research outputs found
Utsu aftershock productivity law explained from geometric operations on the permanent static stress field of mainshocks
The aftershock productivity law, first described by Utsu in 1970, is an
exponential function of the form K=K0.exp({\alpha}M) where K is the number of
aftershocks, M the mainshock magnitude, and {\alpha} the productivity
parameter. The Utsu law remains empirical in nature although it has also been
retrieved in static stress simulations. Here, we explain this law based on
Solid Seismicity, a geometrical theory of seismicity where seismicity patterns
are described by mathematical expressions obtained from geometric operations on
a permanent static stress field. We recover the exponential form but with a
break in scaling predicted between small and large magnitudes M, with
{\alpha}=1.5ln(10) and ln(10), respectively, in agreement with results from
previous static stress simulations. We suggest that the lack of break in
scaling observed in seismicity catalogues (with {\alpha}=ln(10)) could be an
artefact from existing aftershock selection methods, which assume a continuous
behavior over the full magnitude range. While the possibility for such an
artefact is verified in simulations, the existence of the theoretical kink
remains to be proven.Comment: 18 pages, 4 figures (low resolution
Autonomous decision-making against induced seismicity in deep fluid injections
The rise in the frequency of anthropogenic earthquakes due to deep fluid
injections is posing serious economic, societal, and legal challenges to
geo-energy and waste-disposal projects. We propose an actuarial approach to
mitigate this risk, first by defining an autonomous decision-making process
based on an adaptive traffic light system (ATLS) to stop risky injections, and
second by quantifying a "cost of public safety" based on the probability of an
injection-well being abandoned. The ATLS underlying statistical model is first
confirmed to be representative of injection-induced seismicity, with examples
taken from past reservoir stimulation experiments (mostly from Enhanced
Geothermal Systems, EGS). Then the decision strategy is formalized: Being
integrable, the model yields a closed-form ATLS solution that maps a risk-based
safety standard or norm to an earthquake magnitude not to exceed during
stimulation. Finally, the EGS levelized cost of electricity (LCOE) is
reformulated in terms of null expectation, with the cost of abandoned
injection-well implemented. We find that the price increase to mitigate the
increased seismic risk in populated areas can counterbalance the heat credit.
However this "public safety cost" disappears if buildings are based on
earthquake-resistant designs or if a more relaxed risk safety standard or norm
is chosen.Comment: 8 pages, 4 figures, conference (International Symposium on Energy
Geotechnics, 26-28 September 2018, Lausanne, Switzerland
An observational test of the origin of accelerating moment release before large earthquakes
International audience[1] A progressive increase of seismic activity distributed over a wide region around a future earthquake epicenter is termed accelerating moment release (AMR). This phenomenon has been observed in several studies over the last 15 years, although there is no consensus about the physical origin of the effect. In a recent hypothesis known as the stress accumulation (SA) model, the AMR is thought to result from the last stage of loading in the earthquake cycle. In this view, the increasing seismicity is due to minor stress release as the whole region becomes sufficiently stressed for the major event to occur. The stress accumulation model makes specific predictions about the distribution of events in an AMR sequence. Because the AMR is predicted to be a result of loading on the main fault, the precursory activity should be concentrated in the positive lobes of the far-field stresses calculated by a backslip dislocation model of the main shock. To test this model, AMR is first found in optimal circular regions around the epicenters of each of the M w ! 6.5 earthquakes in central and southern California since 1950. A backslip dislocation model is then used to determine which of the precursory events occur in the regions predicted by stress accumulation. AMR is shown to occur preferentially in the lobes of the backslip stress field predicted by the stress accumulation model
STREST – Exploitation plan
The present deliverable contains the detailed dissemination and exploitation plan of the project results, with particular emphasis on communicating to stakeholders and user communities addressing the outcomes of STREST on the enhancement of societal resilience through infrastructure stress tests. This deliverable presents the objectives of the dissemination activities, the identification of stakeholders and the detailed description of tasks concerning the use and dissemination of the STREST project foreground.JRC.G.4-European laboratory for structural assessmen
X-ray and neutron diffraction studies of coupled structural phase transitions in DyBaCoO
A structural transition at K from the to phase
is found to coincide with an anomaly of resistivity. Another structural phase
transition doubling the lattice parameter , which has been postulated
earlier to accompany a low-temperature magnetic transition in
TbBaCoO, is observed in a single crystal DbBaCoO by
means of the X-ray and neutron diffraction. The low temperature phase does not
belong to the space group that has been chosen earlier as the highest
subgroup of the . The transition is of the first order with the
temperature hysteresis, between and K, which
probably explains anomalous magnetic properties in this temperature range.Comment: 6 pages, 4 figure
Optimization of a large-scale microseismic monitoring network in northern Switzerland
We have developed a network optimization method for regional-scale microseismic monitoring networks and applied it to optimize the densification of the existing seismic network in northeastern Switzerland. The new network will build the backbone of a 10-yr study on the neotectonic activity of this area that will help to better constrain the seismic hazard imposed on nuclear power plants and waste repository sites. This task defined the requirements regarding location precision (0.5 km in epicentre and 2 km in source depth) and detection capability [magnitude of completeness Mc= 1.0 (ML)]. The goal of the optimization was to find the geometry and size of the network that met these requirements. Existing stations in Switzerland, Germany and Austria were considered in the optimization procedure. We based the optimization on the simulated annealing approach proposed by Hardt & Scherbaum, which aims to minimize the volume of the error ellipsoid of the linearized earthquake location problem (D-criterion). We have extended their algorithm to: calculate traveltimes of seismic body waves using a finite difference ray tracer and the 3-D velocity model of Switzerland, calculate seismic body-wave amplitudes at arbitrary stations assuming the Brune source model and using scaling and attenuation relations recently derived for Switzerland, and estimate the noise level at arbitrary locations within Switzerland using a first-order ambient seismic noise model based on 14 land-use classes defined by the EU-project CORINE and open GIS data. We calculated optimized geometries for networks with 10-35 added stations and tested the stability of the optimization result by repeated runs with changing initial conditions. Further, we estimated the attainable magnitude of completeness (Mc) for the different sized optimal networks using the Bayesian Magnitude of Completeness (BMC) method introduced by Mignan etal. The algorithm developed in this study is also applicable to smaller optimization problems, for example, small local monitoring networks. Possible applications are volcano monitoring, the surveillance of induced seismicity associated with geotechnical operations and many more. Our algorithm is especially useful to optimize networks in populated areas with heterogeneous noise conditions and if complex velocity structures or existing stations have to be considere
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