Spatial database and website for reservoir-triggered seismicity in Brazil

After confirming that impoundment of large reservoirs could cause earthquakes, studies on reservoir-triggered seismicity (RTS) have had a considerable scientific incentive. Most of the studies determined that the vertical load increase due to reservoir load, and the reduction of effective force due to the increase in pore pressure, can modify the stress field in the reservoir region, possibly triggering earthquakes. In addition, the RTS is conditioned by several factors such as pre-existing tectonic stresses, reservoir height/weight, area-specific geological and hydromechanical conditions, constructive interaction between the orientation of seismotectonic forces, and additional load caused by the reservoir. One of the major challenges in studying RTS is to identify and correlate the factors in the area of influence of the reservoir, capable of influencing the RTS process itself. A spatial seismicity-triggered reservoir database was created to facilitate the research in this field, based on the specifications of the national spatial data infrastructure (INDE), and to assemble data pertinent to the RTS study in the area of reservoirs. In this context, this work presents the procedures and results found in the data processing of seismotectonic factors (dam height, reservoir capacity, lithology, and seismicity) and compared first to the dams that triggered earthquakes and secondly to the Brazilian dam list. The list has been updated with four more cases, making a total of 30 cases. The results indicate that the occurrence of RTS increases significantly with dam height since dams less than 50 m high cause only 2 % of earthquakes while those higher than 100 m cause about 54 %. The reservoir volume also plays a role, and it was estimated that RTS occurrence requires a limiting minimum value of 1×10-4 km3. There was no clear correlation between the geology and geological provinces with RTS. The delayed response time of the reservoirs represents 43 % of the total; that is, almost half of them have hydraulic behavior. The highest magnitude, 4.2, was observed at a reservoir with a volume greater than 10−3 km3. As a practical outcome, to assist the analysis by the general community, the web viewer RISBRA (Reservoir Induced Seismicity in Brazil) was developed to serve as an interactive platform for Reservoir-Triggered Seismicity Database (BDSDR) data.

A Review on the Mechanism of Reservoir-Induced Seismicity for Nepalese Context

Over 90 cases of Reservoir Induced Seismicity have been recorded around the earth. The magnitude was varying from 3.0 to 6.3 on the Richter scale. A Reservoir Induced Seismicity (RIS) can increase the frequency of earthquakes in seismically active zones and cause a shock in seismically inactive zones. Nepal is situated in a seismically active zone with six large earthquakes of magnitude equal to or greater than 7.6. It increases the risk of RIS, while several storage-type hydropower projects are being proposed in Nepal. Seismic activities recorded around the Kulekhani-I reservoir could be a reservoir induced seismicity. However, consistent data of seismic events and reservoir levels during all phases of filling or drawing of water level is missing. This paper reviews the researches on seismic activities caused by reservoirs or tectonic movements, and the need for the study on the mechanism of RIS for the Nepalese context is identified.

Relationship between water level temporal changes and seismicity in the Mingechevir reservoir (Azerbaijan)

<p>Reservoir-induced seismicity has been studied worldwide due to its potential to provoke damage to buildings and constructions, and, more important, human loss. Reservoir-induced seismicity (RIS) is normally related with additional static loading (the weight of the water reservoir and its seasonal variations), tectonic faults, liquefaction and pore pressure variations.The Mingechevir reservoir is located in the north-west of Azerbaijan on the Kurriver. This water reservoir is extended from north-west towards south-east through Kur river valley by 75 km. The area of the dam is 625 km<sup>2</sup> with the average width accounting for 6-8 km. The volume of the dam is 16 km<sup>3</sup>. The dam filling started in 1953. This reservoir is the largest one in the Caucasus and carries a number of geo-hazards interrelated with geodynamics and technogenic factors. The aim of the present study in the Mingechevir reservoir is to investigate relationship between the fluctuations of the water level and the onset of seismicity in the area around the dam more in detail, by using several and independent statistical methods.The temporal variations of the instrumental seismicity (0.5≤M<sub>L</sub>≤3.5) recorded in the Mingechevir area (Azerbaijan) between January 2010 to April 2018 and its relationship with the level variation of the water reservoir was analysed in this study. Due to the relative high completeness magnitude (M<sub>C</sub> = 1.6) of the seismic catalogue of the area, only 136 events were selected over a period of more than 8 years. Thus, the monthly number of events was analysed by using the correlogram-based periodogram, the singular spectrum analysis (SSA) and the empirical mode decomposition (EMD), which are robust against the short size of the time series. Our results point out to the following findings: 1) annual periodicity was found in one SSA reconstructed component of the monthly number of events; 2)quasi-annual periodicity was found in one EMD intrinsic mode function of the monthly number of earthquakes. These obtained results could support in a rigorously statistical manner that the seismicity occurring in Minghechevir area could be triggered by the yearly cycle of the water level of the reservoir.</p><p> </p><p><strong>Keywords:</strong>water reservoir, induced seismicity, water level change, Mingechevir reservoir, Azerbaijan</p>

New insights into the Pertusillo Lake reservoir induced seismicity (Italy) from a high-resolution matched-filter earthquake catalogue

<p>The southern Apennines range hosts a well documented case of protracted Reservoir Induced Seismicity (RIS) associated to the Pertusillo artificial lake. Since the deployment of a local monitoring network in 2001, M3+ swarms were recorded to the south of this medium-sized water reservoir. Interpretation in terms of RIS relies on the positive correlation found between seasonal water level changes and earthquake rate that increases during the winter-spring refill. We present a new high-resolution catalogue of RIS obtained by running a matched-filter (MF) detection technique on data recorded during a dense passive survey between 2005-2006. We aim at producing a very-high quality catalogue in terms of completeness magnitude (Mc) and hypocenter location accuracy to precisely track the spatio-temporal distribution of seismicity, pinpoint the activated faults, investigate the rupture mechanisms and the role played by crustal fluids in triggering RIS. All these issues are critical to improve understanding of the physical mechanism behind the RIS.</p><p>Our initial catalogue includes 406 handpicked templates recorded by 3C 24-stations temporary network run by INGV. Local magnitudes range between 0.06 and 2.63, with a MC of 0.4. Templates are correlated to the 13-month-long data streams by the MF algorithm. A matched event is declared when the average value of cross-correlation function (CC) computed over all stations exceeds 0.65. The procedure furnishes 10056 matched events with associated P- and S-phase automatic picks, weighted according to the uncertainties of template event picks and the CC values of each trace. Matched events are preliminary located in a 1-D model using the NonLinLoc software and then selected based on quality criteria. The final catalog has MC=0.1 and includes 6012 high-quality events with ML > -0.9 that are then relocated through the high-precision double-difference relative technique. We recognize four main clusters confined at 2-6 km depth within a fractured, liquid-bearing carbonate antiform characterized by high-Vp (>6.0 km/s) and very-high Vp/Vs ratio (>2.0) that indicates high-pressure pore fluids. Hypocentral alignments delineate NW-trending high-angle faults dipping to the NE or SW that measure up to 2 km along strike and dip. Prevailing extensional focal mechanisms are coherent with the fault geometry and local stress field. These results suggest re-activation of inherited thrust-faults with associated back-thrusts optimally oriented in the present extensional stress field.  </p><p>The spatiotemporal seismicity distribution indicates a positive correlation between the seasonal oscillation of the lake level and the progressive activation of the 4 clusters of seismicity. Distant clusters from the PWR are delayed with respect to the closer ones, suggesting that seismicity migrates away from the reservoir following a pore fluid pressure triggering process. The b-value is high and it also varies with time between 1.2 and 1.8 with a trend anti-correlated to the lake level. Therefore, the proportion of large earthquakes to small ones increases during the re-fill stage characterized by intense earthquake production and vice-versa. The two southern clusters, more distant from the lake, with events that delineate clear fault-zones, share the lower b-values (1.4).</p>

Website – Spatial database for reservoir-triggered seismicity in Brazil

After confirming that impoundment of large reservoirs could cause earthquakes worldwide, studies on reservoir-triggered seismicity (RTS) have had a considerable scientific incentive. Most of the studies determined that the vertical load increase due to reservoir load, and the reduction of effective effort due to the increase in pore pressure, can modify the stress regime in the reservoir region, possibly triggering earthquakes. In addition, the RTS is conditioned by several factors such as pre-existing tectonic stresses, reservoir size/weight, area-specific geological and hydromechanical conditions, constructive interaction between the orientation of seismotectonic forces, and additional load caused by the reservoir. One of the major challenges for studying RTS is to identify and correlate the factors in the area of influence of the reservoir, capable of influencing the RTS process itself. To assist the research, it was created a spatial seismicity-triggered reservoir database (BDSDR) based on the specifications of the national spatial data infrastructure (INDE), for gathering data pertinent to the RTS study in the area of reservoirs. In this context, this work presents the procedures and results found in the data processing of seismotectonic factors (dam height, reservoir volume, geology, and seismicity level) and compared with the dams that triggered earthquakes and the Brazilian dam catalog, which was then updated from 26 to 30 cases. The results indicate that the occurrence of RTS increases significantly with dam height since dams less than 50 m high cause only 2 % of earthquakes while those higher than 100 m cause about 54 %. The reservoir volume also plays a role and it was estimated that RTS occurrence requires a limiting minimum value of 1 × 10−4 km3. There was no clear correlation between the geology and geological provinces with RTS. The delayed response time of the reservoirs represents 43 % of the total, that is, almost half of them have hydraulic behavior. The highest magnitude, 4.2, was observed for an event that occurred in a reservoir with a volume greater than 10−3 km3. As a practical result to assist the analysis by the general community, the web viewer RISBRA (Reservoir Induced Seismicity in Brazil) was developed to serve as an interactive platform for BDSDR data.