Hypocenter-Based 3D Imaging of Active Faults: Method and Applications in the Southwestern Swiss Alps

Despite the fact that earthquake occurrence can be strongly influenced by the architecture of pre-existing faults, it remains challenging to obtain information about the detailed subsurface geometries of active fault systems. Current geophysical methods for studying such systems often fail to resolve geometrical complexities at sufficiently high spatial resolutions. In this work, we present a novel method for imaging the detailed 3D architectures of seismically active faults based on high-precision hypocenter catalogs, using nearest neighbor learning and principal component analysis. The proposed approach enables to assess variations in fault instabilities and kinematics. We apply the method to the relatively relocated St. Léonard (max. ML = 3.2) and Anzère (max. ML = 3.3) microearthquake sequences in the Southwestern Swiss Alps, revealing strike-slip fault systems with interconnecting stepovers at depths of 3–7 km and lengths ranging from 0.5 to 2 km. In combination with additional information about fault instabilities and kinematics, we observe significantly reduced earthquake migration velocities and fault locking processes within the stepovers. Understanding such processes and their role in the propagation of strain across stepovers is of great relevance, as these structures can potentially limit earthquake ruptures but also represent possible locations for the nucleation of larger ruptures. Our proposed method is expected to be broadly useful for further applications such as monitoring hydraulic fracture stimulations or geothermal exploration of natural, fluid-bearing faults. Conducting similar high-resolution spatiotemporal analyses of microseismic sequences has the potential to greatly enhance our comprehension of how the 3D fault architecture impacts seismogenic fault reactivation.ISSN:2169-9313ISSN:0148-0227ISSN:2169-935

The Effect of Pre-Existing Structures on the Moosfluh Landslide and its Lateral Propagation (Great Aletsch Glacier, Switzerland)

The retreat of the Great Aletsch Glacier is accompanied by a series of slope failures in solid bedrock, which are heavily influenced by the presence of pre-existing deformation structures. Since the 1880's, the Great Aletsch Glacier has shortened by more than 3 km and decreased about 400 m in thickness. As a reaction to the loss of the stabilizing effect of the ice, one of the largest active deep-seated landslides in the European Alps with an affected surface area of about 1.5 km2, called Moosfluh landslide, is evolving. In this study, a multimethod approach combining field work, remote sensing techniques and microseismic monitoring is used to assess the effect of pre-existing structures on the landslide deformation processes. The landslide evolution from 2008 to 2018 could be reconstructed with high spatial resolution. Surface deformation analysis reveals the concentration of high deformation in narrow zones, allowing to directly link pre-existing tectonic and exhumation structures with landslide deformation processes. Toppling as the main gravity-driven process is enabled by reactivation of NE-SW striking, steeply SE dipping Alpine Handegg phase shear zones. Differences in the lateral detachment processes are attributed to shear zone bridges in the NE as well as fractures and shear zones similarly oriented to Alpine Oberaarb phase shear zones in the SW. At the landslide toe, a transition from toppling to sliding mechanism due to the formation of a continuous basal detachment surface can be observed, which is favored by the presence of exfoliation joints. The dramatic acceleration of the Moosfluh landslide in autumn 2016 is directly related to an increase in glacier height loss rate, which implies that glacier retreat is the main trigger of the landslide. A temporal stabilization of the landslide is recorded after 2017, most probably caused by the self-stabilizing properties of flexural toppling. However, microseismic data records a lateral propagation of the landslide, following the retreating Great Aletsch Glacier

Erratum to: Guidelines for the use and interpretation of assays for monitoring autophagy (3rd edition) (Autophagy, 12, 1, 1-222, 10.1080/15548627.2015.1100356

non present