TY - JOUR A1 - Maghsoudi, Samira A1 - Cesca, Simone A1 - Hainzl, Sebastian A1 - Kaiser, Diethelm A1 - Becker, Dirk A1 - Dahm, Torsten T1 - Improving the estimation of detection probability and magnitude of completeness in strongly heterogeneous media, an application to acoustic emission (AE) JF - Geophysical journal international N2 - Reliable estimations of magnitude of completeness (M-c) are essential for a correct interpretation of seismic catalogues. The spatial distribution of M-c may be strongly variable and difficult to assess in mining environments, owing to the presence of galleries, cavities, fractured regions, porous media and different mineralogical bodies, as well as in consequence of inhomogeneous spatial distribution of the seismicity. We apply a 3-D modification of the probabilistic magnitude of completeness (PMC) method, which relies on the analysis of network detection capabilities. In our approach, the probability to detect an event depends on its magnitude, source receiver Euclidian distance and source receiver direction. The suggested method is proposed for study of the spatial distribution of the magnitude of completeness in a mining environment and here is applied to a 2-months acoustic emission (AE) data set recorded at the Morsleben salt mine, Germany. The dense seismic network and the large data set, which includes more than one million events, enable a detailed testing of the method. This method is proposed specifically for strongly heterogeneous media. Besides, it can also be used for specific network installations, with sensors with a sensitivity, dependent on the direction of the incoming wave (e.g. some piezoelectric sensors). In absence of strong heterogeneities, the standards PMC approach should be used. We show that the PMC estimations in mines strongly depend on the source receiver direction, and cannot be correctly accounted using a standard PMC approach. However, results can be improved, when adopting the proposed 3-D modification of the PMC method. Our analysis of one central horizontal and vertical section yields a magnitude of completeness of about M-c approximate to 1 (AE magnitude) at the centre of the network, which increases up to M-c approximate to 4 at further distances outside the network; the best detection performance is estimated for a NNE-SSE elongated region, which corresponds to the strike direction of the low-attenuating salt body. Our approach provides us with small-scale details about the capability of sensors to detect an earthquake, which can be linked to the presence of heterogeneities in specific directions. Reduced detection performance in presence of strong structural heterogeneities (cavities) is confirmed by synthetic waveform modelling in heterogeneous media. KW - Seismic attenuation KW - Statistical seismology Y1 - 2013 U6 - https://doi.org/10.1093/gji/ggt049 SN - 0956-540X VL - 193 IS - 3 SP - 1556 EP - 1569 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Muksin, Umar A1 - Haberland, Christian A1 - Bauer, Klaus A1 - Weber, Michael H. T1 - Three-dimensional upper crustal structure of the geothermal system in Tarutung (North Sumatra, Indonesia) revealed by seismic attenuation tomography JF - Geophysical journal international N2 - The geothermal potential in Tarutung is controlled by both the Sumatra Fault system and young arc volcanism. In this study we use the spatial distribution of seismic attenuation, calculated from local earthquake recordings, to image the 3-D seismic attenuation of the area and relate it with the temperature anomalies and the fluid distribution of the subsurface. A temporary seismic network of 42 stations was deployed around Tarutung and Sarulla (south of Tarutung) for a period of 10 months starting in 2011 May. Within this period, the network recorded 2586 local events. A high-quality subset of 229 events recorded by at least 10 stations was used for the attenuation inversion (tomography). Path-average attenuation (t(p)*) was calculated by using a spectral inversion method. The spread function, the contour lines of the model resolution matrix and the recovery test results show that our 3-D attenuation model (Q(p)) has good resolution around the Tarutung Basin and along the Sarulla graben. High attenuation (low Q(p)) related to the geothermal system is found in the northeast of the Tarutung Basin suggesting fluid pathways from below the Sumatra Fault. The upper part of the studied geothermal system in the Tarutung district seems to be mainly controlled by the fault structure rather than by magmatic activities. In the southwest of the Tarutung Basin, the high attenuation zone is associated with the Martimbang volcano. In the Sarulla region, a low-Q(p) anomaly is found along the graben within the vicinity of the Hopong caldera. KW - Seismicity and tectonics KW - Body waves KW - Seismic attenuation KW - Seismic tomography Y1 - 2013 U6 - https://doi.org/10.1093/gji/ggt383 SN - 0956-540X SN - 1365-246X VL - 195 IS - 3 SP - 2037 EP - 2049 PB - Oxford Univ. Press CY - Oxford ER -