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  • 1
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    Earthquakes in Switzerland and surrounding regions during 2015 and 2016 (2019)
    Details
    Publication Date: 2020-12-07
    Description: This report summarizes the seismicity in Switzerland and surrounding regions in the years 2015 and 2016. In 2015, the Swiss Seismological Service detected and located 735 earthquakes in the region under consideration. With a total of 20 earthquakes of magnitude ML C 2.5, the seismic activity of potentially felt events in 2015 was close to the average of 23 earthquakes over the previous 40 years. Seismic activity was above average in 2016 with 872 located earthquakes of which 31 events had ML C 2.5. The strongest event in the analyzed period was the ML 4.1 Salgesch earthquake, which occurred northeast of Sierre (VS) in October 2016. The event was felt in large parts of Switzerland and had a maximum intensity of V. Derived focal mechanisms and relative hypocenter relocations of aftershocks image a SSE dipping reverse fault, which likely also hosted an ML 3.9 earthquake in 2003. Another remarkable earthquake sequence in the Valais occurred close to Sion with four felt events (ML 2.7–3.2) in 2015/16. We associate this sequence with a system of WNW-ESE striking fault segments north of the Rhoˆne valley. Similarities with a sequence in 2011, which was located about 10 km to the NE, suggest the existence of an en-echelon system of basement faults accommodating dextral slip along the Rhoˆne-Simplon line in this area. Another exceptional earthquake sequence occurred close to Singen (Germany) in November 2016. Relocated hypocenters and focal mechanisms image a SW dipping transtensional fault segment, which is likely associated with a branch of the Hegau-Bodensee Graben. On the western boundary of this graben, micro-earthquakes close to Schlattingen (TG) in 2015/16 are possibly related to a NE dipping branch of the Neuhausen Fault. Other cases of earthquakes felt by the public during 2015/16 include earthquakes in the region of Biel, Vallorcine, Solothurn, and Savognin.
    Description: SwissEnergy (http:// www.energieschweiz.ch) and the Swiss Federal Office of Energy for the financial support of project GEOBEST-CH; Swiss Competence Center for Energy Research—Supply of Electricity (http://www.sccer-soe.ch); Swiss-AlpArray SINERGIA project CRSII2_154434/1 by the Swiss National Science Foundation (SNSF)
    Description: Published
    Description: 221–244
    Description: 2T. Sorgente Sismica
    Description: 1IT. Reti di monitoraggio
    Description: 5IT. Osservatori
    Description: JCR Journal
    Keywords: Seismicity ; Magnitude of completeness ; Focal mechanisms ; Seismotectonics ; Rhone-Simplon line ; Hegau-Bodensee graben ; Basel ; Aar massif ; 04. Solid Earth ; 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
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    Hybrid Broadband Seismograms for Seismic Shaking Scenarios: An Application to the Po Plain Sedimentary Basin (Northern Italy) (2020)
    Springer
    Details
    Publication Date: 2021-06-22
    Description: The densely populated Po Plain, a very deep sedi- mentary basin in northern Italy, is prone to heavy shaking during earthquakes. Seismic hazard assessment must account for local variation in wave amplification. Standard ground motion prediction equations may fail to picture the complexity of strong lateral gradients in seismic response, due to sharp structural heterogeneity. For this reason, there is an increasing demand for full waveform predictions for engineering applications. Here, we present an implementation of a hybrid broadband simulation based on the method of Mai et al. (Bull Seismol Soc Am 100(6):3338–3339, 2010), to obtain complete broadband seismograms of 0.1–10 Hz. With this method, low frequency (〈1 Hz) and high frequency (1–10 Hz) seismograms are simulated separately using a deter- ministic and a stochastic method, respectively. We apply the method to four events recorded within the Po basin, with magnitude ranging from Mw = 4.4 to Mw = 5.6. The low frequency (LF) simulation is performed using SPECFEM3D on a few test sub- surface velocity models. The three-dimensional velocity model MAMBo (Molinari et al. in Bull Seismol Soc Am 105(2A):753–764, 2015)—consisting of a detailed structural description of the basin, based on extensive active-source data, embedded within a regional 3D crustal model—provided the best results for broadband simulations that most closely corresponded with the observations. It performed better than an ambient noise tomography model with more accurate S-wave velocities but less well defined layer topographies, emphasizing the importance of first order velocity discontinuities. The high frequency (HF) seis- mograms are simulated using the multiple scattering approach of Zeng et al. (J Geophys Res Solid Earth 96(B1):607–619, 1991). The scattering coefficients are obtained by performing a non linear inversion for each station to find best fitting synthetic envelopes. HF energy is then combined at 1 Hz to match the amplitude and phase spectra of the LF signal. We are able to simulate full waveforms throughout the Po Plain, of which shaking duration matches observed data for stations located in the basin. Shaking amplitudes are generally overestimated in the low frequency simulation by the MAMBo velocity model. Updating the MAMBo velocity model with more accurate S-wave velocity information of the ambient noise tomography model should improve the fit in future simulations.
    Description: Published
    Description: 2181–2198
    Description: 1T. Struttura della Terra
    Description: JCR Journal
    Keywords: Ground motion ; hybrid method ; sedimentary basin ; Seismic shaking scenario ; 04. Solid Earth
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
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    Unknown
    The 2020 coronavirus lockdown and seismic monitoring of anthropic activities in Northern Italy (2020)
    Nature P. G.
    Details
    Publication Date: 2020-06-11
    Description: In March/April 2020 the Italian government drastically reduced vehicle traffic and interrupted all non-essential industrial activities over the entire national territory. Italy thus became the first country in the world, with the exception of Hubei, to enact lockdown measures as a consequence of the COVID-19 outbreak and the need to contain it. Italy is also a seismically active area, and as such is monitored by a dense permanent network of seismic stations. We analyse continuous seismic data from many stations in northern and central Italy, and quantify the impact of the lockdown on seismic ambient noise, as a function of time and location. We find that the lockdown reduces ambient noise significantly in the 1–10 Hz frequency range; because natural sources of seismic noise are not affected by the lockdown, the seismic signature of anthropic noise can be characterised with unprecedented clarity, by simply comparing the signal recorded before and after the lockdown. Our results correlate well with independent evaluations of the impact of the lockdown (e.g., cell phone displacements), and we submit that ambient-noise seismology is a useful tool to monitor containment measures such as the coronavirus lockdowns.
    Description: European Union Horizon 2020 Research and Innovation Programme, grant agreements 802777-MONIFAULTS.
    Description: Published
    Description: 9404
    Description: 1T. Struttura della Terra
    Description: JCR Journal
    Keywords: ambient noise ; COVID-19 lockdown ; anthropic noise ; seismic monitoring ; 04. Solid Earth ; 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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