Synthetic earthquake catalogs simulating seismic activity in the Corinth Gulf, Greece, fault system

The North-Eastern zone of the Gulf of Corinth in Greece is characterized by the rotation of a micro-plate in formation. The Island Akarnanian Block (IAB) have been progressively individualized since the Pleistocene (less than ~ 1.5 My ago). This micro-plate is the result of a larger-scale tectonic context with, on one side the N-S extension of the Gulf of Corinth to the East, and on the other side the Hellenic subduction to the South and the Apulian collision to the West. To the Northeast, the IAB micro-plate is bounded by a large North-South sinistral strike-slip fault system, the Katouna-Stamna Fault (KSF) and by several normal faults. To the North, normal faults reach the limit between Apulian and Eurasian plates and to the East, they form the East-West graben of Trichonis lake.Although the structures and dynamics behind the Gulf of Corinth extension are today relatively known, nevertheless, the set of faults linking the Gulf of Corinth to the Western subduction structures remain poorly studied. The seismicity recorded by the Greek national network shows discrepancies regarding to the faults mapped on the surface.At the end of 2015, a new micro-seismicity campaign started with the deployment of a temporary seismological network in an area ranging from the Gulf of Patras to the Amvrakikos Gulf toward the North. This network includes 17 seismic stations, recording continuously, added to the permanent stations of the Corinth Rift Laboratory (CRL) and of the Hellenic Unified Seismic Network (HUSN).The analysis of the seismological records is still in process for the 2016 and 2017 years. Our study consists first in picking the P- and S- waves, and then to precisely localize the seismic events recorded by our temporary seismological network combined with the permanent ones. We will present here the event location map obtained for the 2016-2017 period, a new seismic velocity model, and focal mechanisms. The seismic activity including thousands of events, is characterized by the presence of numerous clusters of few days to few weeks duration. The clusters are analysed in detail by relative relocations in order to appraise their physical processes and their implications in the fault activity. We will discuss the deformation mode of the region and build a seismotectonic model consistent with the regional geodynamics and observations.

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Structural complexities and tectonic barriers controlling recent seismic activity of the Pollino area (Calabria-Lucania, Southern Italy) – constraints from stress inversion and 3D fault model building

10.5194/se-2021-76 ◽

2021 ◽

Author(s):

Daniele Cirillo ◽

Cristina Totaro ◽

Giusy Lavecchia ◽

Barbara Orecchio ◽

Rita de Nardis ◽

...

Keyword(s):

Seismic Activity ◽

Model Building ◽

Fault Model ◽

P Wave ◽

Fault System ◽

Double Difference ◽

Seismic Sequence ◽

High Angle ◽

Time Space ◽

Seismological Data

Abstract. The integration of field geology and high-resolution seismological data allowed us to reconstruct the 3D Fault Model of the sources which gave rise to the 2010–2014 Pollino seismic sequence. The model is constrained at the surface by structural geological data which provide the true attitude of the single faults and their cross-cut relationships. At depth, the fault geometry was obtained using the distributions of selected high-quality relocated hypocenters. Relocations were carried out through a non-linear Bayloc algorithm, followed by the double-difference relative location method HypoDD, applied to a 3D P-wave velocity model. Geological and seismological data converge in describing an asymmetric active extensional fault system characterized by an E to NNE-dipping low-angle detachment, with its high-angle synthetic splays, and SW- to WSW-dipping, high-angle antithetic faults. The cluster of hypocenters and the peculiar time-space evolution of the seismic activity highlight that two sub-parallel WSW-dipping seismogenic sources, namely the Rotonda-Campotenese and Morano-Piano di Ruggio faults activated during the seismic crisis. By applying to the activated structures the appropriate earthquake-scaling relationships, based on fault length and fault area, we infer that the maximum expected magnitudes calculated using the fault area are the more reliable. We estimated Mw = 6.4 for the Rotonda-Campotenese and Mw = 6.2 for the Morano-Piano di Ruggio deducing that both the faults did not release their seismic potential during the 2010–2014 seismic sequence. The size of the activated patches, reconstructed by projecting on the 3D seismogenic fault planes the early aftershocks of the seismicity clusters, are consistent with the observed magnitude of the associate strongest events. Finally, we point out that the western segment of the Pollino Fault, despite not being presently active, acts as a barrier to the southern propagation of the Rotonda-Campotenese and Morano-Piano di Ruggio faults, limiting their dimensions and seismogenic potential.

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Physics-Based Simulation of Spatiotemporal Patterns of Earthquakes in the Corinth Gulf, Greece, Fault System

Bulletin of the Seismological Society of America ◽

10.1785/0120210038 ◽

2021 ◽

Author(s):

Rodolfo Console ◽

Roberto Carluccio ◽

Maura Murru ◽

Eleftheria Papadimitriou ◽

Vassilis Karakostas

Keyword(s):

Stress Transfer ◽

Spatial Relation ◽

Fault System ◽

Recurrence Time ◽

Earthquake Catalog ◽

Earthquake Simulation ◽

Strong Earthquakes ◽

Corinth Gulf ◽

Regional Seismicity ◽

Physics Based Simulation

ABSTRACT A physics-based earthquake simulation algorithm for modeling the long-term spatiotemporal process of strong (M ≥ 6.0) earthquakes in Corinth Gulf area, Greece, is employed and its performance is explored. The underlying physical model includes the rate- and state-dependent frictional formulation, along with the slow tectonic loading and coseismic static stress transfer. The study area constitutes a rapidly extending rift about 100 km long, where the deformation is taken up by eight major fault segments aligned along its southern coastline, and which is associated with several strong (M ≥ 6.0) earthquakes in the last three centuries, since when the historical earthquake catalog is complete. The recurrence time of these earthquakes and their spatial relation are studied, and the simulator results reveal spatiotemporal properties of the regional seismicity such as pseudoperiodicity as well as multisegment ruptures of strong earthquakes. As the simulator algorithm allows the display of the stress pattern on all the single elements of the fault, we are focusing on the time evolution of the stress level before, during, and after these earthquakes occur. In this respect, the spatiotemporal variation of the stress and its heterogeneity appear to be correlated with the process of preparation of strong earthquakes in a quantitative way.

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Seismic activity and structural features in the Charlevoix region, Quebec

Canadian Journal of Earth Sciences ◽

10.1139/e87-202 ◽

1987 ◽

Vol 24 (11) ◽

pp. 2118-2129 ◽

Cited By ~ 21

Author(s):

Maurice Lamontagne

Keyword(s):

Seismic Activity ◽

Impact Crater ◽

Time Window ◽

Fault System ◽

Earthquake Risk ◽

Earthquake Activity ◽

Seismic Zone ◽

Nodal Solutions ◽

Data Set ◽

The Impact

The Charlevoix region is historically the most active earthquake zone in eastern Canada. Understanding the links between its seismicity and the faults of the region is important for the assessment of earthquake risk along the St. Lawrence Valley. The region has been monitored by a microseismic array since 1977, yielding accurate locations of the hypocentres. Previous analyses of data from the array indicated a relationship between the earthquakes and the St. Lawrence Valley paleorift faults. As a sequel to previous studies, the relationships between the seismic activity and the faults of the region were reexamined through the use of the composite P-nodal solutions, in an effort to clarify the nature of faulting in the seismic zone. The microseisms were partitioned into subsets of events on the basis of geological and hypocentre-trend considerations. The main objectives of this paper are to delineate the details of faulting within the Charlevoix region and to determine the effect of the impact crater on the nature of faulting in this area.Assuming a constant 6.2 km/s velocity model and using a data set of 107 events, composite fault-plane solutions were computed. The composite P-nodal solutions indicated that the Charlevoix impact crater modifies to a certain extent the focal-mechanism characteristics. Events outside the impact crater were found to be quite consistent in their polarity distribution on the focal sphere, suggesting similarity in their focal mechanisms. The composite mechanism of these events suggests a relationship between the earthquakes and the north–south faults mapped outside the impact crater. The magnitude mb (Lg) 5.0 earthquake of August 19, 1979, the largest event in the selected time window, had different fault planes than some of its aftershocks. Nevertheless, the polarity distribution of the aftershocks was in agreement with the average trend for the events outside the crater. Events inside the impact crater were found to be produced along more variable fault orientations, with an average trend similar to that of the rift fault system. It is proposed that the meteor impact weakened the rift faults and introduced its own fractures. The present earthquake activity probably occurs along these weak fault surfaces. The effect of the impact crater on the type of faulting versus depth is not readily discernible from available data. In general, meteor impacts do not leave neotectonic seismic signatures: the Charlevoix impact crater might represent a different case because of the presence of weakened paleorift faults.

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Visualizing heterogeneities of earthquake hypocenter catalogs: modeling, analysis, and compensation

Progress in Earth and Planetary Science ◽

10.1186/s40645-020-00401-8 ◽

2021 ◽

Vol 8 (1) ◽

Author(s):

Yosihiko Ogata

Keyword(s):

Seismic Activity ◽

Detection Rate ◽

Empirical Bayes ◽

Rate Function ◽

Change Over Time ◽

Detection Rates ◽

Earthquake Catalogs ◽

Earthquake Hypocenter ◽

Large Earthquakes ◽

Over Time

AbstractAs basic data for seismic activity analysis, hypocenter catalogs need to be accurate, complete, homogeneous, and consistent. Therefore, clarifying systematic errors in catalogs is an important discipline of seismicity research. This review presents a systematic model-based methodology to reveal various biases and the results of the following analyses. (1) It is critical to examine whether there is a non-stationary systematic estimation bias in earthquake magnitudes in a hypocenter catalog. (2) Most earthquake catalogs covering long periods are not homogeneous in space, time, and magnitude ranges. Earthquake network structures and seismometers change over time, and therefore, earthquake detection rates change over time and space. Even in the short term, many aftershocks immediately following large earthquakes are often undetected, and the detection rate varies, depending on the elapsed time and location. By establishing a detection rate function, the actual seismic activity and the spatiotemporal heterogeneity of catalogs can be discriminated. (3) Near real-time correction of source locations, far from the seismic observation network, can be implemented based on better determined source location comparisons of other catalogs using the same identified earthquakes. The bias functions were estimated using an empirical Bayes method. I provide examples showing different conclusions about the changes in seismicity from different earthquake catalogs. Through these analyses, I also present actual examples of successful modifications as well as various misleading conclusions about changes in seismic activity. In particular, there is a human made magnitude shift problem included in the global catalog of large earthquakes in the late nineteenth and early twentieth centuries.

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Fault motions at the Baldwin Hills Reservoir site

Bulletin of the Seismological Society of America ◽

10.1785/bssa0550010165 ◽

1965 ◽

Vol 55 (1) ◽

pp. 165-180

Author(s):

Donald E. Hudson ◽

Ronald F. Scott

Keyword(s):

Seismic Activity ◽

Fault System ◽

Motion Information ◽

Ground Movements ◽

The Past ◽

Elevation Changes ◽

The Relationship ◽

Damaging Effects

Abstract A distinction is made between the damaging potential of rapid fault motions associated with earthquakes and those having a relatively slow creep type motion. Information is given on nonseismic movements that have been occurring on faults passing through the Baldwin Hills Reservoir during the past 10 years. The relationship between those faults and the Inglewood fault system is described, and correlations are presented with local elevation changes, horizontal ground movements, and seismic activity. Comparisons are made with similar slow fault motions occurring at other places in California, and attention is drawn to the potential damaging effects of such movements.

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