Tobias Diehl

Last Name

Diehl

First Name

Tobias

ORCID

0000-0001-6264-1506

Organisational unit

02818 - Schweiz. Erdbebendienst (SED) / Swiss Seismological Service (SED)

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Publications1 - 10 of 61

Analysis of induced microseismicity at the geothermal project Schlattingen (Canton Thurgau, Switzerland)
Kraft, Toni; Herrmann, Marcus; Diehl, Tobias (2016)
Nagra Project Report
Earthquakes in Switzerland and surrounding regions during 2015 and 2016
Diehl, Tobias; Clinton, John Francis; Deichmann, Nicolas; et al. (2018)
Swiss Journal of Geosciences
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 ≥ 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 ≥ 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 Rhône 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 Rhône-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.
Potential influence of overpressurized gas on the induced seismicity in the St. Gallen deep geothermal project (Switzerland)
Zbinden, Dominik; Rinaldi, Antonio Pio; Diehl, Tobias; et al. (2020)
Solid Earth
In July 2013, the city of St. Gallen conducted a deep geothermal project that aimed to exploit energy for district heating and generating power. A few days after an injection test and two acid stimulations that caused only minor seismicity, a gas kick forced the operators to inject drilling mud to combat the kick. Subsequently, multiple earthquakes were induced on a fault several hundred meters away from the well, including a ML 3.5 event that was felt throughout the nearby population centers. Given the occurrence of a gas kick and a felt seismic sequence with low total injected fluid volumes (∼1200 m3), the St. Gallen deep geothermal project represents a particularly interesting case study of induced seismicity. Here, we first present a conceptual model based on seismic, borehole, and seismological data suggesting a hydraulic connection between the well and the fault. The overpressurized gas, which is assumed to be initially sealed by the fault, may have been released due to the stimulations before entering the well via the hydraulic connection. We test this hypothesis with a numerical model calibrated against the borehole pressure of the injection test. We successfully reproduce the gas kick and spatiotemporal characteristics of the main seismicity sequence following the well control operation. The results indicate that the gas may have destabilized the fault during and after the injection operations and could have enhanced the resulting seismicity. This study may have implications for future deep hydrothermal projects conducted in similar geological conditions with potentially overpressurized in-place gas.
Seismic monitoring and alert in Switzerland: real- and near-real-time products of the Swiss national seismic networks
Clinton, John Francis; Behr, Yannik; Cauzzi, Carlo; et al. (2014)
Proceedings of the 2nd European Conference on Earthquake Engineering and Seismology (2ECEES)
Earthquakes in Switzerland and surrounding regions during 2019 and 2020
Diehl, Tobias; Cauzzi, Carlo Virgilio; Clinton, John Francis; et al. (2025)
Swiss Journal of Geosciences
This report summarizes the seismicity in Switzerland and surrounding regions in the years 2019 and 2020. In 2019 and 2020, the Swiss Seismological Service detected and located 1660 and 1407 earthquakes in the region under consideration, respectively. The strongest event in the analysed period was the ML 4.3 Elm/Steinibach earthquake, which occurred in the Glarus Alps in eastern Switzerland on October 25, 2020. Received felt reports suggest intensities up to degree V for this earthquake. Modelled and instrumentally measured ground motions, however, hint at intensities approaching degree VI-VII at the epicentre. Derived focal mechanisms and relative hypocentre relocations of fore- and aftershocks image a dextral WSW-ENE to W-E striking multi-segment strike-slip fault zone with a total length of about 3.5 km. Well-constrained focal depths of 1-2 km indicate that the fault zone likely locates in the uppermost part of the crystalline basement of the eastern Aar Massif. Another exceptional earthquake sequence occurred between Anz & egrave;re and Sanetschpass in the Rawil Depression in November 2019. Within 10 days, more than 300 earthquakes occurred in this cluster and 16 of those events reached ML magnitudes between 2.5 and 3.3. Focal mechanisms and relative hypocentre relocations derived for this sequence image the reactivation of a contractional stepover. The imaged stepover confirms the previously proposed segmented nature of the Rawil Fault Zone north of the Rh & ocirc;ne valley in SW Switzerland. The ML 4.2 Novel earthquake, which occurred in the Pr & eacute;alpes region south of Lake Geneva on May 28, 2019, provides additional evidence for the recently proposed domain of NE-SW oriented extensional to transtensional deformation along the Alpine Front in the transition zone between Central and Western Alps. Evidence for transtensional deformation along the SW edge of the Mont-Blanc Massif is provided by another remarkable earthquake cluster near the Grandes Jorasses Mountain in the border region between France and Italy. The transtensional deformation of the Hegau-Bodensee Graben in the northern foreland is revealed by a vigorous earthquake sequence on the Bodanr & uuml;ck Peninsula in southern Germany in 2019. Finally, evidence for unusually shallow seismicity in the domain of the Dent-Blanche nappe is provided by the ML 3.5 Arolla earthquake. In conclusion, the seismic activity during the period 2019-2020 is exceptional in terms of absolute numbers of earthquakes as well as number of events with ML >= 2.5.
Seismotectonic evidence for present-day transtensional reactivation of the slowly deforming Hegau-Bodensee Graben in the northern foreland of the Central Alps
Diehl, Tobias; Madritsch, Herfried; Schnellmann, Michael; et al. (2023)
Tectonophysics
This study presents a seismotectonic analysis of the Miocene-aged Hegau-Bodensee Graben, a major tectonic element in the northern foreland of the European Central Alps. The graben is characterized by comparatively low strain rates and low-to-moderate seismicity. Our study builds on the seismological analysis of earthquakes recorded by a recently densified seismometer network. The derived high-precision absolute and relative hypocenter relocations allow to identify seismogenic structures in the pre-Mesozoic basement, which we relate to bounding faults on either side of the NW-SE striking graben. A cluster of seismicity on the SW side of the graben is associated with the previously mapped Neuhausen Fault. In contrast, the seismogenic, SW-dipping bounding faults on the opposite side of the graben, between the extinct Hegau volcanic field and the Bodanrück peninsula of Lake Constance, cannot be associated with any known fault. A set of 51 focal mechanisms allows for a high-resolution analysis of kinematics and stress regime of the graben. Our results show that the bounding faults of the graben are optimally oriented to be reactivated in transtensional mode in the present-day stress field. Slip rates across the Neuhausen and Randen Faults estimated from geodetic data are likely <0.1 mm/yr. In comparison with historical seismicity over the past 600 years and geomorphic field observations, geodetic rates of 0.1 mm/yr appear overestimated. Nevertheless, historical seismicity suggests that slip rates have the potential to generate MW 5.0 earthquakes within this slowly deforming, transtensional fault zone in the foreland of the Alpine collision zone on timescales of several hundred years.
Using waveform similarity to enhance the long-term analysis of a Swiss geothermal project
Toledo, Tania; Simon, Verena; Kraft, Toni; et al. (2025)
Proceedings of the European Geothermal Congress 2025
In July 2013, a deep geothermal project was initiated in the city of St. Gallen, Switzerland, with the aim of harnessing energy for district heating and power generation. Reservoir stimulations and well-control procedures triggered a seismic sequence, which culminated in a magnitude Mw3.3 (ML3.5) earthquake led by an uncontrolled gas release (a "gas kick"). Following the significant earthquake, the Swiss Seismological Service (SED) conducted a review to assess the extent to which operations may have contributed to the induced seismicity. In addition to automatically detected events, manually identified events were incorporated into near real-time monitoring, with delays of up to 12 hours for smaller events. Early seismicity, however, did not provide clear signs to the unexpected gas influx. Although this post-event assessment did not reveal substantial new information that could have influenced operational decisions at the time, it highlighted the need for improved near-real-time detection and analysis protocols to enhance responsiveness in future geothermal developments. In this study, we present a consistent long-term analysis of the microseismicity associated with the deep geothermal project, with the aim of identifying previously undetected events across the full seismic sequence—including pre- and post-closure periods—using a semi-automatic workflow. Using the continuous data from the most sensitive station (SGT00), we apply template matching with selected representative templates from a manually assembled catalog. We recalculate magnitudes, relocate detected events, and perform a statistical analysis of the seismicity using the in-house software QuakeMatch. Our goal is to refine the understanding of the reservoir’s response to hydraulic changes triggered by project operations and the observed gas kick, using a consistent, semi-automatic approach. More importantly, we investigate the temporal evolution of the induced seismic sequence and assess the potential for ongoing seismicity related to the terminated project, extending the analysis up to the present day.
The AlpArray Research Seismicity-Catalogue
Bagagli, Matteo; Molinari, Irene; Diehl, Tobias; et al. (2022)
Geophysical Journal International
We take advantage of the new large AlpArray Seismic Network (AASN) as part of the AlpArray research initiative (), to establish a consistent seismicity-catalogue for the greater Alpine region (GAR) for the time period 2016 January 1-2019 December 31. We use data from 1103 stations including the AASN backbone composed of 352 permanent and 276 (including 30 OBS) temporary broad-band stations (network code Z3). Although characterized by a moderate seismic hazard, the European Alps and surrounding regions have a higher seismic risk due to the higher concentration of values and people. For these reasons, the GAR seismicity is monitored and routinely reported in catalogues by a 11 national and 2 regional seismic observatories. The heterogeneity of these data set limits the possibility of extracting consistent information by simply merging to investigate the GAR's seismicity as a whole. The uniformly spaced and dense AASN provides, for the first time, a unique opportunity to calculate high-precision hypocentre locations and consistent magnitude estimation with uniformity and equal uncertainty across the GAR. We present a new, multistep, semi-automatic method to process ~50 TB of seismic signals, combining three different software. We used the SeisComP3 for the initial earthquake detection, a newly developed Python library ADAPT for high-quality re-picking, and the well-established VELEST algorithm both for filtering and final location purposes. Moreover, we computed new local magnitudes based on the final high-precision hypocentre locations and re-evaluation of the amplitude observations. The final catalogue contains 3293 seismic events and is complete down to local magnitude 2.4 and regionally consistent with the magnitude 3+ of national catalogues for the same time period. Despite covering only 4 yr of seismicity, our catalogue evidences the main fault systems and orogens' front in the region, that are documented as seismically active by the EPOS-EMSC manually revised regional bulletin for the same time period. Additionally, we jointly inverted for a new regional minimum 1-D P-wave velocity model for the GAR and station delays for both permanent station networks and temporary arrays. These results provide the base for a future re-evaluation of the past decades of seismicity, and for the future seismicity, eventually improving seismic-hazard studies in the region. Moreover, we provide a unique, consistent seismic data set fundamental to further investigate this complex and seismically active area. The catalogue, the minimum 1-D P-wave velocity model, and station delays associated are openly shared and distributed with a permanent DOI listed in the data availability section.
Revisiting moment tensors in Switzerland: Unraveling source characteristics in Central Alps and their foreland
Mesimeri, Maria; Diehl, Tobias; Clinton, John Francis; et al. (2022)
EGUsphere
Studies on moment tensors (MT) and focal mechanisms are of great importance for assessing regional and local seismotectonic processes, especially when a high-quality, dense network is in operation. However, common MT inversion methods are largely restricted to magnitudes > 3.5. In order to lower the completeness of MT catalogs, improved Green’s functions and/or hybrid inversion techniques are needed. In this study, we revisit small-to-moderate earthquakes, which occurred in Switzerland and surrounding regions by means of various MT inversion methods and assess the potential to improve completeness of MT catalogs in Central Alps region. To accomplish this, we implement state-of the art methods for MT inversion using either full waveform data or combinations of first-motion polarities with amplitudes and amplitude ratios. Methods based on full waveform inversion considered in this study are ISOLA (Sokos & Zahradnik 2013) and Grond (Heimann et al. 2018), as well as techniques based on amplitudes and/or polarities (HybridMT (Kwiatek et al. 2016), MTfit (Pugh & White 2018)), which can solve MTs for smaller magnitude earthquakes. Hence, the combination of multiple techniques allows to compute full or deviatoric MTs for a broader range of magnitudes and enrich the existing catalogs. We first apply these methods to recent earthquake sequences occurred in the Central Alps between 2019 and 2021. During that period, several earthquake sequences, like the one associated with the 2021 M4.1 Arolla earthquake, occurred and show complexity on the waveforms, due to their shallow focal depths. In addition, several of the standard MT solutions calculated by the Swiss Seismological Service (SED) for these earthquakes indicate complex moment tensors with unusually high percentage of the CLVD component. To check whether such CLVD component is real and not an artifact caused, for instance, by unmodeled heterogeneities, we invert for full and deviatoric MTs using multiple 1D velocity models and algorithms. Additionally, we perform MT inversions for several earthquakes either within selected earthquake sequences or regional background seismicity. The resulting MT solutions are compared to existing high-quality focal mechanisms computed using first motion polarities as well as to high-precision double difference locations. Uncertainties of MT solutions are estimated using bootstrap-based methods. This work contributes towards an enriched high-quality focal mechanisms database for Switzerland, which could be used to revisit the regional to local stress field at unprecedented resolution and provides new insights into the complexities of active fault systems in the Central Alps region.
Climate-change-induced seismicity: The recent onset of seasonal microseismicity at the Grandes Jorasses, Mont Blanc Massif, France/Italy
Simon, Verena; Kraft, Toni; Maréchal, Jean-Christophe; et al. (2025)
Earth and Planetary Science Letters
Modeling studies indicate that the geosphere can dynamically respond to climate change, increasing geological and geomorphological hazards. One such hazard is climate-driven seismicity due to hydrological changes, though observational evidence supporting this phenomenon remains scarce. We present the first dataset linking climate-change-induced snow/glacier melt to increased seismic hazard. Using a template-matching-enhanced catalog (2006–2022), we analyze the ongoing Grandes Jorasses Earthquake Sequence (GJES, Mont Blanc Massif, France/Italy; M_L≤3.1/M_W≤2.9), which exhibits a sudden onset of strong annual periodicity in fall 2015. Our relocations identify seismicity along a major fault zone outcropping in the Mont Blanc Tunnel, where runoff and isotope data suggest that inflow is dominated by young surface meltwater. Modeling meltwater infiltration with a 1D-hydraulic diffusion constrained by the S2M meteorological snowpack model confirms that most of the GJES seismicity can be meltwater-induced. Additionally, our statistical analysis reveals a migratory seismicity component, hosting the largest events. While initially triggered by seasonal meltwater, this component expands primarily via a tectonic mechanism affected by aseismic slip. We attribute the onset of increased and periodic seismicity in 2015 to intensified climate-change-driven heat waves affecting the Mont Blanc Massif's high-altitude cryosphere. Retreating permafrost and glaciers alter meltwater-infiltration pathways, inducing pore-pressure changes that trigger seismicity in new source areas. During peak meltwater-driven seismicity, the seismic hazard levels can rise by two orders of magnitude compared to pre-2015 levels. Our findings suggest that climate change can significantly elevate the local seismic hazard in alpine regions. This phenomenon may affect other glaciated areas globally, highlighting the need for improved seismic risk assessment for impacted alpine communities.

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Tobias Diehl

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