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We developed a multi-step assessment scheme for improved site selection during seismic network installation in densely populated areas. Site selection is a complex process where different aspects (seismic background noise, geology, and financing) have to be taken into account. In order to improve this process, we developed a step-wise approach that allows quantifying the quality of a site by using, in addition to expert judgement and test measurements, two weighting functions as well as reference stations. Our approach ensures that the recording quality aimed for is reached and makes different sites quantitatively comparable to each other. Last but not least, it is an easy way to document the decision process, because all relevant parameters are listed, quantified, and weighted. Our assessment scheme incorporates seven fundamental steps: First, potential sites are identified and pre-evaluated in the office (step 1). Second, potential sites are visited during a site survey (step 2) and then classified using the first weighting function (step 3) that identifies those sites most suitable for test measurements (step 4). Test measurements are conducted and analyzed in order to quantify seismic background noise and site effects. The results of the analysis are evaluated using the second weighting function (step 6). Finally, the overall quality is assessed (step 7) by using reference stations and pre-defined quality benchmarks to insure that chosen sites are suitable for the designated monitoring purpose. We demonstrate the multi-step assessment scheme by applying it to a densification of an existing seismic network.

This report of the Swiss Seismological Service summarizes the seismic activity in Switzerland and surrounding regions during 2013. During this period, 699 earthquakes and 208 quarry blasts were detected and located in the region under consideration. With a total of 18 events with local magnitudes ML ≥ 2.5, the seismic activity in the year 2013 was slightly below the average over the previous 38years. Most noteworthy were the two earthquake sequences of St. Gallen (SG) in July and Balzers (FL) in December. The former was induced by reservoir stimulation operations at the St. Gallen geothermal project. The maximum local magnitude in the sequence was 3.5, comparable in size with the ML 3.4 event induced by stimulation operations below Basel in 2006. The sequence of Balzers was associated with an ML 4.1 earthquake in the border region to Liechtenstein. More than 30 aftershocks with magnitudes ranging between ML −0.2 and ML 3.7 were detected in the month following the mainshock. The ML 3.5 St. Gallen and the ML 4.1 Balzers earthquakes were widely felt by the public but no reports on damages are known. The maximum intensity for both events was IV.

This report of the Swiss Seismological Service summarizes the seismic activity in Switzerland and surrounding regions during 2009. During this period, 450 earthquakes and 68 quarry blasts were detected and located in the region under consideration. The three strongest events occurred about 15km NW of Basel in southern Germany (ML 4.2), near Wildhaus in the Toggenburg (ML 4.0) and near Bivio in Graubünden (ML 3.5). Although felt by the population, they were not reported to have caused any damage. With a total of 24 events with ML≥2.5, the seismic activity in the year 2009 was close to the average over the previous 34years

This report of the Swiss Seismological Service summarizes the seismic activity in Switzerland and surrounding regions during 2005. During this period, 611 earthquakes, 96 quarry blasts and two landslides were detected and located in the region under consideration. With 19 events with ML ≥ 2.5, the seismic activity in the year 2005 was below the average over the last 30 years. However, with the earthquake of Vallorcine (ML 4.9) located just across the border to France, between Martigny and Chamonix, and the two earthquakes of Rumisberg and Brugg (ML 4.1), located in the lower crust beneath the Jura Mountains of northern Switzerland, the year 2005 saw three events that produced shaking of intensity IV and V (EMS98). Of the 611 recorded earthquakes more than 110 events are aftershocks of the Vallorcine quake. Moreover, 51 events occurred within two days at the end of August during a period of very intense rainfalls. The epicenters of these events were concentrated in several clusters distributed over a wide area of central Switzerland, and their focal depths were shallow, so that they most likely constitute a case of precipitationinduced seismicity

This report of the Swiss Seismological Service summarizes the seismic activity in Switzerland and surrounding regions during 2012. During this period, 497 earthquakes and 88 quarry blasts were detected and located in the region under consideration. With a total of only 13 events with ML≥2.5, the seismic activity in the year 2012 was far below the average over the previous 37years. Most noteworthy were the earthquake sequence of Filisur (GR) in January with two events of ML 3.3 and 3.5, the ML 4.2 and ML 3.5 earthquakes at a depth of 32km below Zug in February and the ML 3.6 event near Vallorcine in October. The epicentral intensity of the ML 4.2 event close to Zug was IV, with a maximum intensity of V reached in a few areas, probably due to site amplification effects

A series of 112 earthquakes was recorded between October 2005 and August 2007 during the excavation of the MFS Faido, the southernmost access point of the new Gotthard Base Tunnel. Earthquakes were recorded at a dense network of 11 stations, including 2 stations in the tunnel. Local magnitudes computed from Wood-Anderson-filtered horizontal component seismograms ranged from −1.0 to 2.4; the largest earthquake was strongly felt at the surface and caused considerable damage in the tunnel. Hypocenter locations obtained routinely using a regional 3-D P-wave velocity model and a constant Vp/Vs ratio 1.71 were about 2km below the tunnel. The use of seismic velocities calibrated from a shot in the tunnel revealed that routinely obtained hypocenter locations were systematically biased to greater depth and are now relocated to be on the tunnel level. Relocation of the shot using these calibrated velocities yields a location accuracy of 25m in longitude, 70m in latitude, and 250m in focal depth. Double-difference relative relocations of two clusters with highly similar waveforms showed a NW-SE striking trend that is consistent with the strike of mapped faults in the MFS Faido. Source dimensions computed using the quasidynamic model of Madariaga (Bull Seismo Soc Am 66(3):639-666, 1976) range from 50 to 170m. Overlapping source dimensions for earthquakes within the two main clusters suggests that the same fault patch was ruptured repeatedly. The observed seismicity was likely caused by stress redistribution due to the excavation work in the MFS Faido

This report of the Swiss Seismological Service summarizes the seismic activity in Switzerland and surrounding regions during 2006. During this period, 572 earthquakes and 91 quarry blasts were detected and located in the region under consideration. Of these earthquakes, two occurred in conjunction with the construction of the new Gotthard railway tunnel and 165 were induced artificially by the stimulation of a proposed geothermal reservoir beneath the city of Basel. With 20 events with M L ≥ 2.5, five of which were artificially induced, the seismic activity in the year 2006 was far below the average over the previous 31 years. Nevertheless, six events were felt by the public, most prominently the strongest of the induced Basel events (M L 3.4), which caused some non-structural building damage. Noteworthy are also the two earthquakes near Cortaillod (M L 3.2), on the shore of Lake Neuchâtel, and in Val Mora (M L 3.5), between the Engadin and Val Müstair, as well as the 42 aftershocks of the M L 4.9 Vallorcine earthquake, between Martigny and Chamonix, of September 2005

One-dimensional (1D) velocity models are still widely used for computing earthquake locations at seismological centers or in regions where three-dimensional (3D) velocity models are not available due to the lack of data of sufficiently high quality. The concept of the minimum 1D model with appropriate station corrections provides a framework to compute initial hypocenter locations and seismic velocities for local earthquake tomography. Since a minimum 1D model represents a solution to the coupled hypocenter-velocity problem it also represents a suitable velocity model for earthquake location and data quality assessment, such as evaluating the consistency in assigning pre-defined weighting classes and average picking error. Nevertheless, the use of a simple 1D velocity structure in combination with station delays raises the question of how appropriate the minimum 1D model concept is when applied to complex tectonic regions with significant three-dimensional (3D) variations in seismic velocities. In this study we compute one regional minimum 1D model and three local minimum 1D models for selected subregions of the Swiss Alpine region, which exhibits a strongly varying Moho topography. We compare the regional and local minimum 1D models in terms of earthquake locations and data quality assessment to measure their performance. Our results show that the local minimum 1D models provide more realistic hypocenter locations and better data fits than a single model for the Alpine region. We attribute this to the fact that in a local minimum 1D model local and regional effects of the velocity structure can be better separated. Consequently, in tectonically complex regions, minimum 1D models should be computed in sub-regions defined by similar structure, if they are used for earthquake location and data quality assessment

We present a new approach to relocate earthquakes in the greater western Alpine region using main crustal phases (Pg, Pn, PmP) that takes advantage of recent developments in P-wave velocity models and modelling of the Moho topography in the region, as well as the ability to track reflected and refracted phases in three-dimensional (3-D) heterogeneous media. Our approach includes a new 3-D P-wave velocity model for Switzerland and surrounding regions that combines a first-order Moho discontinuity based on local earthquake tomography (LET) and controlled-source seismology (CSS) information and 3-D seismic velocity information based on LET. Traveltimes for the main crustal phases (Pg, Pn, PmP) are computed using a fast marching method. We use a non-linear, probabilistic approach to relocate earthquakes that has been extended to include the use of secondary phases. We validate our approach using synthetic data, which was computed for a real earthquake and different combinations of available phases (Pg, Pn, PmP). We also applied our approach to relocate four selected earthquakes, two shallow and two deep crustal events in the northern Alpine foreland, for which independent information (ground truth information) on their focal depths exist. Our results demonstrate that the precision and accuracy of focal depth estimates can be greatly improved if secondary phases are used. This gain is a combined effect of an improved range of take-off angles and the use of differential traveltimes between first and secondary arriving phases. Our results also show that reliable information on the Moho depth is crucial to obtain accurate focal depths, if Pn or PmP phases are used in the relocation process. Finally, our approach demonstrates that proper identification of the main crustal phases in combination with an appropriate model parametrization in the forward solver will significantly improve earthquake locations

We present a newly developed approach of combining controlled-source seismology (CSS) and local earthquake tomography (LET) data to obtain a new 3-D crustal model of the western Alpine region. Our approach combines either data by taking into account the strengths of the individual seismic methods. Our western Alpine 3-D model is primarily based on a well-defined Moho, constrained by CSS and LET data, and includes smooth lateral variations in seismic velocities mainly constrained by LET data, but locally also by CSS data. The consistent combination of results from the two different seismic methods is feasible due to LET Moho elements, as defined by characteristic P-wave velocities and their uncertainty estimates. These uncertainty estimates are based on values of the diagonal element of the resolution matrix, absolute P-wave velocities that are typical for crust and mantle and a specific velocity gradient across the Moho discontinuity. Finally, our definition of LET Moho elements and their uncertainties is validated by comparisons of highest quality Moho results from both methods coinciding in 353 localities. Our model clearly shows three Moho surfaces, being Europe, Adria and Liguria as well as major tectonic structures like suture zones and the high-velocity Ivrea body. In general, it is in a good agreement with previous studies. The biggest differences occur along plate boundaries, where the strong lateral velocity variations are best resolved by LET. Due to the larger number of available Moho reflector elements a more accurate definition of plate boundaries at Moho level is possible and, therefore, new insights in deep lithosphere structures of the Alpine collision zone can be expected. Furthermore, our new 3-D crustal model directly includes a 3-D migrated image of the Ivrea body

During summer 2011, seismic activity in the ablation zone of the western Greenland ice sheet (GrIS) was monitored using a network of three-component seismometers. The seismic record includes a large variety of icequakes and seismic tremors that demonstrate a clear correlation with subglacial water flow. We verified the existence of well-known shallow icequakes (related to surface crevasse formation), deep icequakes (located at 100–160m depth) and narrow-banded short-term seismic tremors (tens of seconds in duration). In addition, we present previously unreported long-term tremors lasting several hours. Using attenuation of the measured tremor amplitude, we locate the epicentre of this long-term tremor to a large moulin within our study area. Between 3 and 11 Hz, our continuous seismic record is dominated by this ‘moulin tremor’ and shows strong correlation with the water level of the generating moulin. We argue that monitoring of icequake and glacial tremor sources bears high potential for investigating glacier hydraulics and dynamics, and is thus an ideal supplement to traditional glaciological measurements.