scholarly journals Modeling seismicity rate changes along the Hellenic subduction Zone (Greece).

2016 ◽  
Vol 47 (3) ◽  
pp. 1157
Author(s):  
M. K. Leptokaropoulos ◽  
E. E. Papadimitriou ◽  
B. Orlecka–Sikora ◽  
G. V. Karakostas ◽  
F. Vallianatos
Keyword(s):  
Subduction Zone ◽  
Parameter Determination ◽  
Physical Parameters ◽  
Coulomb Stress Changes ◽  
Seismicity Rate ◽  
Hellenic Subduction Zone ◽  
Seismicity Rates ◽  
Stress Changes ◽  
Seismicity Rate Changes ◽  
Constitutive Parameters

The Dieterich (1994) Rate/State formulation was applied for the seismicity rate changes in the western part of the Hellenic arc to be investigated. The completeness magnitude of the shallow seismicity (h<60km) was firstly evaluated for different time windows. The spatio-temporal changes of these seismicity rates (reference rates) were studied then for the interevent periods between successive strong(M≥6.0) earthquakes. These changes were correlated with the Coulomb stress changes (ΔCFF) produced by the stronger events, through a Rate/State model which incorporates physical parameters associated with fault dynamics such as the tectonic stressing rate, fault constitutive parameters and frictional response of the rupture zones. The influence of the former parameters in the model performance wastested by evaluating the linear correlation coefficient between modeled and real earthquake production rates along with their confidence limits. Application of different parameter values was attempted for the sensitivity of the calculated seismicity rates and their fit to the real data to be tested. Given the geographical peculiarity of the Hellenic Subduction zone, that yields to high uncertainties in the earthquake focal parameter determination, the results demonstrate that the present formulation and the available data sets are sufficient enough to contribute to a robust seismic hazard assessment. 

scholarly journals SEISMICITY RATE CHANGES IN ASSOCIATION WITH TIME DEPENDENT STRESS TRANSFER IN THE REGION OF NORTHERN AEGEAN SEA, GREECE

2017 ◽  
Vol 43 (4) ◽  
pp. 2093
Author(s):  
K. M. Leptokaropoulos ◽  
E. E. Papadimitriou ◽  
B. Orlecka–Sikora ◽  
V. G. Karakostas
Keyword(s):  
Stress Field ◽  
Stress Transfer ◽  
Seismic Hazard Assessment ◽  
Aegean Sea ◽  
Occurrence Rate ◽  
Coulomb Stress Changes ◽  
Seismicity Rate ◽  
Stress Changes ◽  
Before And After ◽  
Seismicity Rate Changes

The region of northern Aegean has suffered several strong earthquakes since the beginning of the 20th century, causing extensive damage and loss of lives. For the seismic hazard assessment in the area, several studies have been accomplished, among them being the ones dealing with the Coulomb stress changes due to the seismic slip caused by major earthquakes, in addition with the constant tectonic loading on the major regional faults. The aim of the present study is to evaluate if seismicity rate changes from 1964 to 2008 are associated with changes in the stress field. For this purpose the stronger events (Μw>5.8) that occurred in this period were considered and their contribution to the stress field evolution was investigated by calculations performed just before and after their occurrence. This influence was then examined in connection with the occurrence rate of small events (Μw > 3.8) for the respective time intervals. After defining the probability density function (PDF) of the small events distribution, a rate/state model was used to correlate static stress changes with seismicity rate and to compare the observed with the expected seismicity rate for each time period.

scholarly journals Stress and pore fluid pressure control of seismicity rate changes following the 2016 Kumamoto earthquake, Japan Version 2021125

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Kodai Nakagomi ◽  
Toshiko Terakawa ◽  
Satoshi Matsumoto ◽  
Shinichiro Horikawa
Keyword(s):  
Focal Mechanism ◽  
Fluid Pressure ◽  
Pore Fluid ◽  
2016 Kumamoto Earthquake ◽  
Pore Fluid Pressure ◽  
Seismicity Rate ◽  
Kumamoto Earthquake ◽  
The 2016 Kumamoto Earthquake ◽  
Seismicity Rates ◽  
Seismicity Rate Changes

AbstractWe quantitatively examined the influence of pore fluid pressure and coseismic stress changes on the seismicity rate changes that followed the 2016 Kumamoto earthquake, on the basis of two approaches. One is a numerical calculation of the classic stress metric of ∆CFS, and the other is an inversion analysis of pore fluid pressure fields with earthquake focal mechanism data. The former calculation demonstrated that seismicity rate changes were consistent with the expectation from ∆CFS in 65% of the target region, whereas they were not in the remaining 35% of the region. The latter analysis indicates that seismicity rates increased in the regions where pore fluid pressure before the Kumamoto earthquake sequence was remarkably enhanced above hydrostatic, regardless of values of ΔCFS. This suggests that the increase in pore fluid pressure is one of the important physical mechanisms triggering aftershock generation. We obtained evidence that pore fluid pressure increased around the southern part of the main rupture zone after the mainshock, examining temporal changes in types of focal mechanism data. The average increases in pore fluid pressure were estimated to be 17, 20, and 17 MPa at depths of 5, 10, and 15 km, respectively. These large increases in pore fluid pressure cannot be explained under the undrained condition. The spatial derivative of the pore fluid pressure field in the depth direction implies that fluid supply from greater depths may have controlled increases in seismicity rates that followed the large earthquake.

scholarly journals SEISMICITY CHANGES DETECTION DURING THE SEISMIC SEQUENCES EVOLUTION AS EVIDENCE OF STRESS CHANGES

2017 ◽  
Vol 43 (4) ◽  
pp. 1994
Author(s):  
A.C. Astiopoulos ◽  
E. Papadimitriou ◽  
V. Karakostas ◽  
D. Gospodinov ◽  
G. Drakatos
Keyword(s):  
Temporal Distribution ◽  
Aftershock Sequence ◽  
Occurrence Rate ◽  
Generation Process ◽  
Seismicity Rate ◽  
Seismic Sequences ◽  
Epidemic Type Aftershock Sequence ◽  
Stress Changes ◽  
Lefkada Island ◽  
Seismicity Rate Changes

The statistical properties of the aftershock occurrence are among the main issues in investigating the earthquake generation process. Seismicity rate changes during a seismic sequence, which are detected by the application of statistical models, are proved to be precursors of strong events occurring during the seismic excitation. Application of these models provides a tool in assessing the imminent seismic hazard, oftentimes by the estimation of the expected occurrence rate and comparison of the predicted rate with the observed one. The aim of this study is to examine the temporal distribution and especially the occurrence rate variations of aftershocks for two seismic sequences that took place, the first one near Skyros island in 2001 and the second one near Lefkada island in 2003, in order to detect and determine rate changes in connection with the evolution of the seismic activity. Analysis is performed through space–time stochastic models which are developed, based upon both aftershocks clustering studies and specific assumptions. The models applied are the Modified Omori Formula (MOF), the Epidemic Type Aftershock Sequence (ETAS) and the Restricted Epidemic Type Aftershock Sequence (RETAS). The modelling of seismicity rate changes, during the evolution of the particular seismic sequences, is then attempted in association with and as evidence of static stress changes

scholarly journals Significance test for seismicity rate changes before the 1987 Chiba-toho-oki earthquake (M 6.7) Japan

1999 ◽  
Vol 42 (5) ◽  
Author(s):  
K. Maeda ◽  
S. Wiemer
Keyword(s):  
Quantitative Analysis ◽  
Real Time ◽  
Rate Increase ◽  
Significance Test ◽  
Seismic Quiescence ◽  
Rupture Zone ◽  
Seismicity Rate ◽  
Seismicity Rates ◽  
Seismicity Rate Changes ◽  
Precursory Seismic Quiescence

A precursory seismic quiescence lasting 1.5 ± 0.5 years was observed prior to the 1987 M 6.7 Chiba-toho-oki earthquake, Central Japan. This event was the largest mainshock to occur in the region in 60 years. A quantitative analysis of the seismicity rates, using two independent catalogs provided by the NIED and JMA networks, shows that the precursory seismic quiescence is centered in the shallower part of the rupture zone of the subsequent mainshock, at a depth of 20-40 km. At the hypocenter of the 1987 Chiba-toho-oki mainshock, a 50% increase in the seismicity rate was detected in the NIED data, coinciding in time with the onset of quiescence (1986.4 ± 0.5). The simultaneous appearance of both quiescence in the shallow part of the rupture zone observed in two catalogs, and a rate increase in the immediate hypocenter region, suggest that these phenomena are causally linked to the subsequent mainshock. However, a quantitative analysis of both catalogs reveals that the precursory quiescence and rate increase are not unique, since rate changes of this duration and significance often occur in the data. A rate change of this significance rating could probably not be detected as a precursor in a real time approach. For the aid of real time monitoring of seismicity rate changes, we introduce the method to calculate the 95-percentile of confidence level for the significant rate changes.

scholarly journals Can Hydrocarbon Extraction From the Crust Enhance or Inhibit Seismicity in Tectonically Active Regions? A Statistical Study in Italy

2021 ◽  
Vol 9 ◽  
Author(s):  
Alexander Garcia ◽  
Licia Faenza ◽  
Andrea Morelli ◽  
Ilaria Antoncecchi
Keyword(s):  
Large Scale ◽  
Oil And Gas ◽  
Active Regions ◽  
Rate Reduction ◽  
Oil And Gas Development ◽  
Hydrocarbon Production ◽  
Seismicity Rate ◽  
Seismicity Rates ◽  
Stress Changes ◽  
Tectonically Active

A number of oil- and gas-producing leases have been operating in Italy in the last decades, many of which are located in the surroundings of tectonically active regions. Identifying human-induced seismicity in areas with high levels of natural seismicity is a difficult task for which virtually any result can be a source of controversy. We implemented a large-scale analysis aiming at tracking significant departures of background seismicity from a stationary behavior around active oil and gas development leases in Italy. We analyzed seismicity rates before and after hydrocarbon peak production in six oil-producing and 43 gas-producing leases, and evaluate the significance of possible seismicity rate changes. In a considerable number of cases seismicity rate results stationary. None of the observed cases of seismicity rate increase after the peak production is statistically significant (at a s.l. = 0.05). Conversely, considering cases of seismicity rate decrease after peak production, our results suggest that the seismicity rate reduction is statistically significant (s.l. = 0.05) around one oil-producing lease (Val d’Agri, Basilicata) and around a cluster of gas-producing leases in Sicily. Our results put in evidence correlated changes between the rates of shallow seismicity and hydrocarbon production in these areas, which are then identified as hotspots requiring more detailed research; assessing actual causal relationships between these processes will require further physically-based modelling. If a physical causative link between these processes exists, then the observed seismicity rate reduction could either be due to increased seismicity during the progressive increase in production before reaching its maximum, or to an actual seismicity rate reduction after that peak. Considering that there is evidence of seismicity occurring before the start of hydrocarbon production, which contrasts with the evident reduction of events observed after the peak production, we think it likely that the seismicity inhibition is a plausible hypothesis. Using a simple model we also calculate Coulomb stress changes in planes optimally oriented for failure, and we show that under some conditions the inhibition of seismicity is feasible in at least one of these cases. We conclude that more efforts to study the mechanisms and the possible consequences of anthropogenically-driven seismicity inhibition are required.

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