Groundwater extraction-induced seismicity around Delhi region, India

The non-tectonic deformation, either of natural or anthropogenic origin, may influence the earthquake occurrence process and seismicity rate along the plate-boundary or ‘stable’ plate-interiors domains. The low magnitude but moderate seismicity rate of Delhi region on the stable plate-interiors domains of India, exhibits significant variation both in short-term at annual seasonal scale and in long-term at decadal scale. It correlates with the anthropogenic groundwater pumping for the extensive irrigation, urban activities, and seasonally controlled hydrological loading cycle of Indo-Ganga Basin hosted freshwater aquifers. Our coupled hydro-mechanical simulation and poro-mechanical analysis of basement fault stability suggest that the combined aquifer contraction and basement rock expansion act together to modulate the effective stress regime and anthropogenic seismicity on the basement faults in Delhi region.

Seismicity at Newdigate, Surrey, during 2018–2019: A Candidate Mechanism Indicating Causation by Nearby Oil Production

During 2018–2019, oil was intermittently produced from the Late Jurassic Upper Portland Sandstone in the Weald Basin, southeast England, via the Horse Hill-1 and Brockham-X2Y wells. Concurrently, a sequence of earthquakes of magnitude ≤3.25 occurred near Newdigate, ∼3 km and ∼8 km from these wells. The pattern, with earthquakes concentrated during production from this Portland reservoir, suggests a cause-and-effect connection. It is proposed that this seismicity occurred on a patch of fault transecting permeable Dinantian limestone, beneath the Jurassic succession of the Weald Basin, hydraulically connected to this reservoir via this permeable fault and the permeable calcite ‘beef’ fabric within the Portland sandstone; oil production depressurizes this reservoir and draws groundwater from the limestone, compacting it and ‘unclamping’ the fault, reaching the Mohr-Coulomb failure criterion and causing seismicity. In principle this model is fully testable, but required data, notably the history of pressure variations in the wells, are not currently in the public domain. Quantitative estimates are, nonetheless, made of the magnitudes of the variations, arising from production from each well, in the state of stress on the seismogenic Newdigate fault. The general principles of this model, including the incorporation of poroelastic effects and effects of fault asperities into Mohr-Coulomb failure calculations, may inform understanding of anthropogenic seismicity in other settings.

Reliability tests of moment tensor inversion of anthropogenic seismicity

<p>Seismic moment tensor becomes part of basic seismic data processing. For anthropogenic events mostly common and available method to determine mechanism is amplitude inversion. However essential for correct amplitude inversion are good quality data. Factors commonly occurring in anthropogenic seismicity like high noise to signal ratio, low magnitude and shortage of seismic stations with unfavorable focal coverage can introduce undetected errors to inversion solution. In this work, synthetic tests for two seismic networks are presented to examine the reliability of P-wave first peak amplitude inversion for these areas. The synthetic tests of the noise influence on the results of full MT solutions were carried out for two surface networks monitoring anthropogenic seismicity: VERIS network in Vietnam and LUMINEOS network in Poland. Various mechanisms with double couple component variability from 10% to 100% were considered to take into account mechanisms caused by different types of human activity. High variability of solutions in tests shows that some spurious components cannot be avoided in full moment tensor solutions obtained for presented networks in certain cases.</p><p>This work was partially supported by research project no. 2017/27/B/ST10/01267, funded by the National Science Centre, Poland, under agreement no. UMO-2017/27/B/ST10/01267.</p>

Integrating Data under the European Plate Observing System from the Regional and Selected Local Seismic Networks in Poland

High-quality and open-access seismic data are of great importance for both research and increasing public awareness of actual seismic hazards and risks. We present four seismic networks that currently operate in Poland: the backbone Polish Seismological Network (PLSN), which monitors natural teleseismic events as well as regional events from Poland, and three networks that mainly serve the monitoring of anthropogenic seismicity. The acquired data from all four networks are openly available through the European Plate Observing System (EPOS) Information Technology (IT) facilities: the PLSN data within the Observatories and Research Facilities for European Seismology–European Integrated Data Archive and the anthropogenic seismicity data episodes through the induced seismicity-EPOS platform of EPOS Thematic Core Service Anthropogenic Hazards. For each network, we describe briefly the recorded seismic activity, the equipment and composition of the network, the acquisition system, and the data availability. Information from recent studies is used to demonstrate the scientific potential of the acquired anthropogenic seismicity data.

The Finnish National Seismic Network: Toward Fully Automated Analysis of Low-Magnitude Seismic Events

We present an overview of the seismic networks, products, and services in Finland, northern Europe, and the challenges and opportunities associated with the unique combination of prevailing crystalline bedrock, low natural intraplate seismic background activity, and a high level of anthropogenic seismicity. We introduce national and local seismic networks, explain the databases, analysis tools, and data management concepts, outline the Finnish macroseismic service, and showcase data from the 2017 M 3.3 Liminka earthquake in Ostrobothnia, Finland.

On the Portability of ML–Mc as a Depth Discriminant for Small Seismic Events Recorded at Local Distances

We show that ML–Mc is a viable and regionally portable depth discriminant, and therefore may contribute to nuclear test ban treaty verification. A recent study found that the difference between local magnitude (ML) and coda duration magnitude (Mc) discriminates shallow seismic events (mining blasts, mining‐induced earthquakes, and shallow tectonic earthquakes) from deeper tectonic earthquakes in the Utah region. The shallow seismic events had anomalously high Mc values, with increasingly negative ML–Mc values as depth decreased. Here, we evaluate the performance of ML–Mc as a depth discriminant in three new regions and find that ML–Mc increases between 0 and 9 km depth in all cases. Initially, we investigated ML–Mc as a function of depth for naturally occurring earthquakes in the region around Yellowstone National Park, as recorded by the University of Utah Seismograph Stations. For 3358 Yellowstone earthquakes with well‐constrained depths, we found ML–Mc increased 0.030±0.007 magnitude units (m.u.) for each 1 km increase in depth up to 10 km depth. Next, we examined ML–Mc values for anthropogenic seismicity in northern Oklahoma and southern Kansas, as recorded by the National Earthquake Information Center. For 1628 events with well‐constrained depths, we computed a slope for ML–Mc of 0.022±0.010 m.u./km. Finally, we analyzed ML–Mc for 28,722 well‐located earthquakes in Italy, as recorded by the National Institute of Geophysics and Volcanology, and found an ML–Mc slope of 0.018±0.001 m.u./km. In each case, the quoted error bounds represent 95% confidence regions that exclude zero, implying that the depth dependence of ML–Mc is statistically significant. We performed several robustness tests in which we varied the criterion used to define a well‐constrained depth and the depth range used in the linear fit. In nearly all cases, we found a positive slope for ML–Mc versus depth at a confidence level above 95%.