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Kraft T.,Swiss Seismological Service
EAGE/DGG Workshop: Microseismic Monitoring | Year: 2014

We have developed an optimization algorithm for seismic monitoring networks in urban areas that allows to design and evaluate seismic network geometries for arbitrary geotechnical operation layouts. The algorithm is based on the optimization on the simulated annealing approach proposed by Hardt & Scherbaum (1994), which aims to minimize the volume of the error ellipsoid of the linearized earthquake location problem (D-criterion). We have extended their algorithm to: (1) calculate traveltimes of seismic body waves using a finite difference ray tracer and the 3-D velocity model (2) calculate seismic body-wave amplitudes at arbitrary stations assuming the Brune source model and using scaling and attenuation relations recently derived for Switzerland, and (3) 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 use the Bayesian Magnitude of Completeness (BMC) method introduced by Mignan et al.(2011) to estimate the expected magnitude of completeness (Mc) level for the optimal network. Source

Brenguier F.,French National Center for Scientific Research | Rivet D.,University of Nice Sophia Antipolis | Obermann A.,Swiss Seismological Service | Nakata N.,Stanford University | And 4 more authors.
Journal of Volcanology and Geothermal Research | Year: 2016

Monitoring magma pressure buildup at depth and transport to surface is a key point for improving volcanic eruption prediction. Seismic waves, through their velocity dependence to stress perturbations, can provide crucial information on the temporal evolution of the mechanical properties of volcanic edifices. In this article, we review past and ongoing efforts for extracting accurate information of temporal changes of seismic velocities at volcanoes continuously in time using records of ambient seismic noise. We will first introduce the general methodology for retrieving accurate seismic velocity changes from seismic noise records and discuss the origin of seismic velocity temporal changes in rocks. We will then discuss in a second part how noise-based monitoring can improve our knowledge about magmatic activity at a long (years) to a short (days) time scale taking example from Piton de la Fournaise volcano (La Réunion). We will also mention ongoing efforts for operational noise-based seismic monitoring on volcanoes. Further, we will discuss perspectives for improving the spatial localization of detected velocity changes at depth with a special focus on the use of dense seismic arrays. In the last part, we will finally explore the complex response of volcanic regions to seismic shaking with an example from Japan and show how imaging seismic velocity susceptibility allows characterizing the state of pressurized fluids in volcanic regions. © 2016 Elsevier B.V. Source

Cakt E.,Bogazici University | El-Hussain I.,Sultan Qaboos University | Sesetyan K.,Bogazici University | Deif A.,Sultan Qaboos University | And 4 more authors.
Natural Hazards | Year: 2016

This study presents research toward the development of ground-shaking maps after a real earthquake, or for scenario earthquakes originating from seismic sources within and around the Sultanate of Oman. Major important earthquake sources that are important for the Sultanate of Oman are the Makran zone, the Zagros zone, the Zendan-Minab system, the Oman Mountain zone, the Owen fracture zone and the Gulf of Aden zone. The earthquakes that take place on these zones, particularly those from Makran, already resulted and are likely to result in ground-shaking levels that may be significant for the country. The hazard module of software package ELER was customized for use in the development of shake maps in the Sultanate of Oman. For this purpose, (1) major active faults and systems within and around Oman were defined and implemented; (2) ground-motion prediction equations suitable for use and representative of tectonic conditions in Oman were identified and implemented; (3) the effect of local site conditions in resulting ground-shaking levels was attended by implementing the Vs30 maps into ELER methodology; and (4) scripts were developed for the consideration of ground-motion data coming from strong motion stations and from seismometers in and around Oman. They were used in the adjustment of ground-motion distribution maps, such as peak ground acceleration, peak ground velocity and spectral acceleration maps produced using ground-motion prediction equations. Example runs of different scenarios reflecting the use of newly adopted information are presented. © 2016 Springer Science+Business Media Dordrecht Source

Biedermann A.R.,ETH Zurich | Kunze K.,ETH Zurich | Zappone A.S.,Swiss Seismological Service | Hirt A.M.,ETH Zurich
IOP Conference Series: Materials Science and Engineering | Year: 2015

The magnetic fabric of a rock, defined by the anisotropy of magnetic susceptibility (AMS), is often used as a tectonic indicator. In order to establish a quantitative relationship between AMS and mineral texture, it is important to understand the single crystal intrinsic AMS of each mineral that contributes to the AMS of the rock. The AMS and crystallographic preferred orientation (CPO) of amphiboles, olivine and pyroxenes has been analyzed in a series of amphibolites, peridotites and pyroxenites that do show preferred mineral alignment. The CPO of each mineral phase was determined based on electron backscatter diffraction (EBSD). Whole- rock AMS was computed based on the CPO and single crystal AMS of the respective minerals. A comparison between measured and modelled magnetic anisotropy shows that the directions of the principal susceptibility axes agree well in amphibolite and peridotite. Pyroxenite is a good example for competing AMS fabrics in polyphase rocks. © Published under licence by IOP Publishing Ltd. Source

Evans K.F.,ETH Zurich | Zappone A.,Swiss Seismological Service | Kraft T.,Swiss Seismological Service | Deichmann N.,Swiss Seismological Service | Moia F.,RSE Ricerca Sistema Energetico S.p.A.
Geothermics | Year: 2012

The paper documents 41 European case histories that describe the seismogenic response of crystalline and sedimentary rocks to fluid injection. It is part of an on-going study to identify factors that have a bearing on the seismic hazard associated with fluid injection. The data generally support the view that injection in sedimentary rocks tends to be less seismogenic than in crystalline rocks. In both cases, the presence of faults near the wells that allow pressures to penetrate significant distances vertically and laterally can be expected to increase the risk of producing felt events. All cases of injection into crystalline rocks produce seismic events, albeit usually of non-damaging magnitudes, and all crystalline rock masses were found to be critically stressed, regardless of the strength of their seismogenic responses to injection. Thus, these data suggest that criticality of stress, whilst a necessary condition for producing earthquakes that would disturb (or be felt by) the local population, is not a sufficient condition. The data considered here are not fully consistent with the concept that injection into deeper crystalline formations tends to produce larger magnitude events. The data are too few to evaluate the combined effect of depth and injected fluid volume on the size of the largest events. Injection at sites with low natural seismicity, defined by the expectation that the local peak ground acceleration has less than a 10% chance of exceeding 0.07. g in 50 years, has not produced felt events. Although the database is limited, this suggests that low natural seismicity, corresponding to hazard levels at or below 0.07. g, may be a useful indicator of a low propensity for fluid injection to produce felt or damaging events. However, higher values do not necessarily imply a high propensity. © 2011 Elsevier Ltd. Source

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