The Saint-Ursanne earthquakes of 2000 revisited: evidence for active shallow thrust-faulting in the Jura fold-and-thrust belt

The interpretation of seismotectonic processes within the uppermost few kilometers of the Earth’s crust has proven challenging due to the often significant uncertainties in hypocenter locations and focal mechanisms of shallow seismicity. Here, we revisit the shallow seismic sequence of Saint-Ursanne of March and April 2000 and apply advanced seismological analyses to reduce these uncertainties. The sequence, consisting of five earthquakes of which the largest one reached a local magnitude (ML) of 3.2, occurred in the vicinity of two critical sites, the Mont Terri rock laboratory and Haute-Sorne, which is currently evaluated as a possible site for the development of a deep geothermal project. Template matching analysis for the period 2000–2021, including data from mini arrays installed in the region since 2014, suggests that the source of the 2000 sequence has not been persistently active ever since. Forward modelling of synthetic waveforms points to a very shallow source, between 0 and 1 km depth, and the focal mechanism analysis indicates a low-angle, NNW-dipping, thrust mechanism. These results combined with geological data suggest that the sequence is likely related to a backthrust fault located within the sedimentary cover and shed new light on the hosting lithology and source kinematics of the Saint-Ursanne sequence. Together with two other more recent shallow thrust faulting earthquakes near Grenchen and Neuchâtel in the north-central portion of the Jura fold-and-thrust belt (FTB), these new findings provide new insights into the present-day seismotectonic processes of the Jura FTB of northern Switzerland and suggest that the Jura FTB is still undergoing seismically active contraction at rates likely < 0.5 mm/yr. The shallow focal depths provide indications that this low-rate contraction in the NE portion of the Jura FTB is at least partly accommodated within the sedimentary cover and possibly decoupled from the basement.

On the seismicity and tectonic activity Of the Bengal basin

The tectonic activity of the Bengal basin for years 1850-1988 of seismicity and 16 years (1970-1985) of P-wave first motion data have been studied. The seismicity studies reveal three seismic belts such as Dhubri fault (striking N-S), Calcutta hinge zone (striking NE-SW) and the central region of the Bengal basin (striking NW-SE). Dauki fault is comparatively less seismically active than Dhubri fault. The seismicity of Dhubri fault and Calcutta hinge zone are confined to limited extension. The seismic activity along the central portion of the Bengal basin is extending from the Himalayan region (27°N, 88.5°E) to eastern plate margin (23.8°N, 92°E). .This appears to be a tectonic belt and is associated with the northeast drifting of Indian plate. The focal, mechanism studies reveal thrust faulting showing the stresses to be perpendicular to the proposed belt.

Late Quaternary active faulting on the inherited Baoertu basement fault within the eastern Tian Shan orogenic belt: Implications for regional tectonic deformation and slip partitioning, NW China

The deformation pattern and slip partitioning related to oblique underthrusting of the Tarim Basin in the eastern Tian Shan orogenic belt are not well understood because interior deformation images are lacking. The Baoertu fault is an E-W−striking, ∼350-km-long reactivated basement structure within the eastern Tian Shan. In this study, we quantify its late Quaternary activity based on interpretations of detailed high-resolution remote sensing images and field investigations. Three field observation sites along an ∼80-km-long fault segment indicate that the Baoertu fault is characterized by sinistral thrust faulting. Based on surveying of the displaced geomorphic surfaces with an unmanned drone and dating of the late Quaternary sediments using radiocarbon and optically stimulated luminescence (OSL) methods, we estimate a late Quaternary left-lateral, strike-slip rate of 1.87 ± 0.29 mm/yr and a N−S shortening rate of 0.26 ± 0.04 mm/yr for this fault. The lithospheric Baoertu fault acts as a decoupling zone and accommodates the left-lateral shearing caused by the oblique underthrusting of the Tarim Basin. In the eastern Tian Shan orogenic belt, the oblique convergence is partitioned into thrust faulting across the entire range and sinistral slip faulting on the high-dip basement structure within the orogen. This active faulting pattern in the eastern Tian Shan of sinistral shearing in the center and thrust faulting on both sides can be viewed as giant, crustal-scale positive flower structures.

Earthquake Swarm Analysis around Mt. Salak, West Java, Indonesia, Using BMKG Data from August 10 to November 24, 2019

Earthquake swarms commonly come approximately active tectonic and volcanic area. Interestingly, the swarm events occurred ~23 km southwest from Mt. Salak-Bogor, West Java, Indonesia, from August 10 to November 24, 2019, and were recorded by local/regional network of the Indonesian Agency for Meteorology, Climatology, and Geophysics (BMKG). Our previous study showed that in this area a destructive ML 4.6 earthquake with thrust faulting occurred on September 8, 2012. The double-difference method was applied to update the hypocenter locations from the BMKG data. In the time period of ~3.5 months, we relocated 79 swarm events with ~9.4 km depth average for local magnitude (ML) 2.2 to 4.2. The source mechanism result for selected events shows a strike-slip faulting. Our interpretation is that these swarm events are probably related to stress change due to volcano-tectonic activity.

New Analog Experiment for Convergent Regime an example of planet Mercury

&lt;div&gt; &lt;div&gt; &lt;div&gt; &lt;div&gt; &lt;div&gt; &lt;div&gt; &lt;div&gt; &lt;div&gt; &lt;p&gt;We conduct a series of experiments to understand the nature of thrust faulting as a result of global thermal contraction in planetary bodies such as Mercury. The spatial scales and patterns of faulting due to contraction are still not very well understood. However, the problem is complicated even for the homogeneous case where the crustal thickness and material properties do not vary spatially. Previous research showed that the thrust faulting patterns are non-random and are arranged in long systems. This is probably due to the regional-scale stress patterns interacting with each other, leading to the creation of coherent structures. We first conduct 1-Axis experiments where we simulate the contraction of the substratum using an elastic ribbon. On top of this we place the material for which the friction, cohesion and thickness can be controlled for each experiment. The shared interface between the frictional-cohesive material and the shortening elastic substratum dictates undulations and finally the generation of slip planes in the upper layer. We discuss the spatial distribution of these patterns spatially. We then speculate the interaction of such patterns on a 2D plane.&lt;/p&gt; &lt;/div&gt; &lt;/div&gt; &lt;/div&gt; &lt;/div&gt; &lt;/div&gt; &lt;/div&gt; &lt;/div&gt; &lt;div&gt;&amp;#160;&lt;/div&gt; &lt;/div&gt;&lt;div&gt; &lt;div&gt;&amp;#160;&lt;/div&gt; &lt;/div&gt;

Dominant strike-slip faulting and near-constant stress drop of induced earthquakes in the Kiskatinaw area, northeastern British Columbia, Canada

&lt;p&gt;&lt;span&gt;An increasing number of hydraulic fracturing (HF) operations in&amp;#173; low-permeable tight shales in the Kiskatinaw area, northeastern British Columbia, have been associated with M3+ earthquakes in the last decade, including a M&lt;sub&gt;L&lt;/sub&gt; 4.5 on 11/30/2018 near Dawson Creek. Here, we use a catalog of 8285 events ranging from magnitude ML -0.5 to 4.5 between July 2017 and July 2020 to investigate their source parameters. We identify event families using waveform cross-correlation and event temporal correlation, and estimate the focal mechanism solutions (FMS) of the highest-magnitude event within each family using the probabilistic earthquake source inversion framework &lt;/span&gt;&lt;span&gt;&lt;em&gt;Grond&lt;/em&gt;&lt;/span&gt;&lt;span&gt;. We also estimate FMS for events with a magnitude larger than M&lt;/span&gt;&lt;sub&gt;&lt;span&gt;L&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; 2.5 that do not belong to a family (independent events). We compile a FMS catalog using the robustly constrained solutions for the largest events, and associate all smaller earthquakes with a cross-correlation coefficient (CCC) &gt; 0.8 with the corresponding FMS. In addition, we estimate seismic moment and static stress drop values using spectral fitting methods on both single spectra and spectral ratios, and investigate their scaling relations.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;span&gt;In total, we constrain 65 FMS, of which 53 are clustered events, and the remaining 12 are independent events. An additional 4255 events have a CCC &gt; 0.8 with one of the constrained FMS and are listed accordingly in the catalog. Of the total 4320 FMS, 93% are strike-slip events with one nodal plane at low angles to S&lt;/span&gt;&lt;sub&gt;&lt;span&gt;H&lt;/span&gt;&lt;/sub&gt;&lt;span&gt;, 3% are dominantly strike-slip with thrust-faulting components, and the remaining 4% have a dominantly thrust-faulting mechanisms perpendicular to S&lt;/span&gt;&lt;sub&gt;&lt;span&gt;H. &lt;/span&gt;&lt;/sub&gt;&lt;span&gt; The thrust-style events comprise the relatively larger magnitudes contained in the catalog, and may indicate slip on pre-existing faults. Most strike-slip events are part of an event family with multiple matching waveforms, while most thrust-faulting events are isolated with a low number of matching waveforms. &lt;/span&gt;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;span&gt;We fit the spectral corner frequency of 2360 P-phases and 1981 S-phases using single spectra estimates, and 1031 P-phases and 919 S-phases using the spectral ratios. While results from spectral ratios suggest a roughly constant stress drop of ~1 MPa for all magnitudes, the constant stress drop trend from single spectrum fitting breaks down at magnitudes smaller ~ M&lt;/span&gt;&lt;sub&gt;&lt;span&gt;L&lt;/span&gt;&lt;/sub&gt;&lt;span&gt; 2.0, as has commonly been observed for events recorded by surface stations. We do not observe significant dependence of stress-drop values with the faulting style, nor with event depth. &lt;/span&gt;&lt;/p&gt;