Non-stationarity and internal correlations of the occurrence process of mining-induced seismic events

A point process, e.g., the seismic process, is potentially predictable when it is non-stationary, internally correlated or both. In this paper, an analysis of the occurrence process of mining-induced seismic events from Rudna copper mine in Poland is presented. Stationarity and internal correlation are investigated in complete seismic time series and segmentally in subseries demonstrating relatively stable seismicity rates. It is shown that the complete seismic series are non-stationary; however, most of their shorter subseries become stationary. In the stationary subseries, the distribution of interevent time is closer to the exponential distribution, which is characteristic for the Poisson process. However, in most of these subseries, the differences between the interevent time and Poisson distributions are still significant, revealing correlations among seismic events

Seismicity properties of the Chain Transform Fault inferred using data from the PI-LAB experiment

Oceanic transform faults are intriguing in that they do not produce earthquakes as large as might be expected given their dimensions. We use 1-year of local seismicity (370 events above MC = 2.3) recorded on an array of ocean bottom seismometers (OBSs) and geophysical data to study the seismotectonic properties of the Chain transform, located in the equatorial Mid-Atlantic. We extend our analysis back in time by considering stronger earthquakes (MW ≥ 5.0) from global catalogs. We divide Chain into three areas (east, central, and west) based on historical event distribution, morphology, and multidimensional OBS seismicity cluster analysis. Seismic activity recorded by the OBS is the highest at the eastern area of Chain where there is a lozenge-shaped topographic high, a negative rMBA gravity anomaly, and only a few historical MW ≥ 5.5 events. OBS seismicity rates are lower in the western and central areas. However, these areas accommodate the majority of seismic moment release, as inferred from both OBS and historical data. Higher b-values are significantly correlated with lower rMBA and with shallower bathymetry, potentially related to thickened crust. Our results suggest high lateral heterogeneity along Chain. Patches with moderate to low OBS seismicity rates that occasionally host MW ≥ 6.0 earthquakes are interrupted by segments with abundant OBS activity but few historical events with 5.5 ≤ MW < 6.0. This segmentation is possibly due to variable fluid circulation and alteration, which may also change in time

Broad fault zones enable deep fluid transport and limit earthquake magnitudes

Constraining the controlling factors of fault rupture is fundamental to understanding the earthquake cycle. Fluids can influence earthquake locations and magnitudes, although the exact pathways of fluids through the lithosphere are not well-known. Ocean transform faults are an ideal laboratory to study the factors controlling fault ruptures and fluid pathways given their relative simplicity. Here, we analyse seismicity recorded by the Passive Imaging of the Lithosphere-Asthenosphere Boundary (PI-LAB) experiment, centred around the Chain Fracture Zone. We find that earthquakes beneath mapped morphological transpressional features occur deeper than the brittle-ductile transition predicted by simple thermal models but elsewhere occur shallower. These features are characterised by multiple parallel fault segments and step overs, high b-values, gaps in large historical earthquakes, and seismic velocity structures consistent with hydrothermal alteration. This suggests that broader fault damage zones preferentially facilitate fluid transport into the lithosphere. Although this cools the mantle, it also reduces the potential for large earthquakes at punctuated locations (barriers). These barriers divide the transform into asperity segments that are shorter, thereby limiting the earthquake magnitudes in these regions

Seasonal trends and relation to water level of reservoir-triggered seismicity in Song Tranh 2 reservoir, Vietnam

Reservoir-triggered seismicity (RTS) has the potential to generate disastrous seismic events of M6 and bigger. Song Tranh 2 (STR2) is an artificial water reservoir located in Central Vietnam. High seismic activity has been observed in this area since the reservoir was first filled in 2011. The relation between water level and seismic activity in the Song Tranh area is complex, and previous studies have led to the conclusion that ongoing STR2 seismic activity is an example of the delayed response type of RTS. However, the first phase of the activity observed after impoundment has been deemed a rapid response type. There were three stages of the reservoir filling periods: first, a period of initial impoundment, hereinafter referred to as pre-gap period (from 05/01/2011 to 10/06/2012), then a gap period (from 10/06/2012 to 31/08/2013) where reservoir impoundment stopped and water was drained to minimum exploitation level, and finally, a third post-gap period (from 31/08/2013 to 19/06/2017). In this work, we prove that the gap in the filling of reservoir results to a 2-fold rise of seismicity rate. The re-filling of the reservoir results to a drop of activity rate, roughly equal to the pre-gap period, accompanied by a significant increase of b-value. As a consequence, after the gap, the exceedance probability is significantly lower in comparison to pre-gap and gap periods. We also proved that the seismicity recorded between 2013 and 2016 manifested seasonal trends related to water level changes during wet and dry seasons. The response of activity and its delay with respect to water level changes suggest that the main triggering factor is pore pressure change due to the significant water level changes observed. The findings indicate that water load and related pore pressure changes considerably influence seismic activity and stress orientation in this area.</p

Time-dependent seismic hazard in Bobrek coal mine, Poland, assuming different magnitude distribution estimations

The purpose of this study is to evaluate seismic hazard parameters in connection with the evolution of mining operations and seismic activity. The time-dependent hazard parameters to be estimated are activity rate, Gutenberg–Richter b-value, mean return period and exceedance probability of a prescribed magnitude for selected time windows related with the advance of the mining front. Four magnitude distribution estimation methods are applied and the results obtained from each one are compared with each other. Those approaches are maximum likelihood using the unbounded and upper bounded Gutenberg–Richter law and the non-parametric unbounded and non-parametric upper-bounded kernel estimation of magnitude distribution. The method is applied for seismicity occurred in the longwall mining of panel 3 in coal seam 503 in Bobrek colliery in Upper Silesia Coal Basin, Poland, during 2009–2010. Applications are performed in the recently established Web-Platform for Anthropogenic Seismicity Research, available at https://tcs.ah-epos.eu/

An open data infrastructure for the study of anthropogenic hazards linked to georesource exploitation

Abstract Mining, water-reservoir impoundment, underground gas storage, geothermal energy exploitation and hydrocarbon extraction have the potential to cause rock deformation and earthquakes, which may be hazardous for people, infrastructure and the environment. Restricted access to data constitutes a barrier to assessing and mitigating the associated hazards. Thematic Core Service Anthropogenic Hazards (TCS AH) of the European Plate Observing System (EPOS) provides a novel e-research infrastructure. The core of this infrastructure, the IS-EPOS Platform (tcs.ah-epos.eu) connected to international data storage nodes offers open access to large grouped datasets (here termed episodes), comprising geoscientific and associated data from industrial activity along with a large set of embedded applications for their efficient data processing, analysis and visualization. The novel team-working features of the IS-EPOS Platform facilitate collaborative and interdisciplinary scientific research, public understanding of science, citizen science applications, knowledge dissemination, data-informed policy-making and the teaching of anthropogenic hazards related to georesource exploitation. TCS AH is one of 10 thematic core services forming EPOS, a solid earth science European Research Infrastructure Consortium (ERIC) (www.epos-ip.org)