Vasiliki Mouslopoulou - Academia.edu (original) (raw)

Papers by Vasiliki Mouslopoulou

Geophysical Journal International, Nov 25, 2020

Clusty is a new open source toolbox dedicated to earthquake clustering based on waveforms recorde... more Clusty is a new open source toolbox dedicated to earthquake clustering based on waveforms recorded across a network of seismic stations. Its main application is the study of active faults and the detection and characterization of faults and fault networks. By using a density-based clustering approach, earthquakes pertaining to a common fault can be recognized even over long fault segments, and the first-order geometry and extent of active faults can be inferred. Clusty implements multiple techniques to compute a waveform based network similarity from maximum cross-correlation coefficients at multiple stations. The clustering procedure is designed to be transparent and parameters can be easily tuned. It is supported by a number of analysis visualization tools which help to assess the homogeneity within each cluster and the differences among distinct clusters. The toolbox returns graphical representations of the results. A list of representative events and stacked waveforms facilitate further analyses like moment tensor inversion. Results obtained in various frequency bands can be combined to account for large magnitude ranges. Thanks to the simple configuration, the toolbox is easily adaptable to new data sets and to large magnitude ranges. To show the potential of our new toolbox, we apply Clusty to the aftershock sequence of the M w 6.9 25 October 2018 Zakynthos (Greece) Earthquake. Thanks to the complex tectonic setting at the western termination of the Hellenic Subduction System where multiple faults and faulting styles operate simultaneously, the Zakynthos data set provides an ideal case-study for our clustering analysis toolbox. Our results support the activation of several faults and provide insight into the geometry of faults or fault segments. We identify two large thrust faulting clusters in the vicinity of the main shock and multiple strike-slip clusters to the east, west and south of these clusters. Despite its location within the largest thrust cluster, the main shock does not show a high waveform similarity to any of the clusters. This is consistent with the results of other studies suggesting a complex failure mechanism for the main shock. We propose the existence of conjugated strikeslip faults in the south of the study area. Our waveform similarity based clustering toolbox is able to reveal distinct event clusters which cannot be discriminated based on locations and/or timing only. Additionally, the clustering results allows distinction between fault and auxiliary planes of focal mechanisms and to associate them to known active faults.

Journal Of Geophysical Research: Solid Earth, 2017

In this study we utilize regional and teleseismic earthquake moment tensor solutions in order to ... more In this study we utilize regional and teleseismic earthquake moment tensor solutions in order to infer the contemporary crustal stress in the Greek region. We focus on crustal earthquakes and select only solutions with good waveform fits and well-resolved nodal planes. A data set of 1614 focal mechanisms is used as input to a regional-scale damped stress inversion algorithm over a grid whose node spacing is 0.35°. Several resolution and sensitivity tests are performed in order to ascertain the robustness of our results. Our findings show that for most of the Greek region the largest principal stress σ 1 is vertically oriented and that the minimum principal stress axis σ 3 are subhorizontal with a predominant N-S orientation. In the SW Peloponnese the orientation of σ 3 axes rotates clockwise and in SE Aegean counterclockwise. These results are in agreement with the generally accepted model that slab rollback combined with gravitational spreading of the Aegean lithosphere are the main causes of the extension. Transitions between different faulting types in NW Greece or in the Aegean occur within narrow zones in the order of tens of kilometers. A visual comparison of the principal horizontal stress axes and the principal strain axes derived from GPS observations shows good agreement, suggesting that the crust in the Greek region behaves largely in an elastic manner.

EGU General Assembly Conference Abstracts, Apr 1, 2019

The 2016 M w 7.8 Kaikōura Earthquake (South Island, New Zealand) caused widespread complex ground... more The 2016 M w 7.8 Kaikōura Earthquake (South Island, New Zealand) caused widespread complex ground deformation including significant coastal uplift of rocky shorelines. This coastal deformation is used here to develop a new methodology, in which intertidal marine biota have been calibrated against tide-gauge records to quantitatively constrain predeformation biota living depths relative to sea level. This living depth is then applied to biologically measured tectonic uplift at three other locations along the Kaikōura coast. We also test how tectonic uplift measured using this calibrated marine biota compares to vertical deformation measured, at the same localities, using instrumental methods [Light Detection and Ranging (LiDAR) and strong motion data], and non-calibrated biological methods. Data show that where biological data is collected by RTK-GNSS in sheltered locations, this new tide-gauge calibration method estimates tectonic uplift with an accuracy of +/-≤0.07 m in the vicinity of the tide-gauge, and an overall mean accuracy of +/-0.10 m or 10% compared to differential LiDAR methods for all locations. Sites exposed to high wave wash, or data collected by tape-measure, are more likely to show higher uplift results. Tectonic uplift estimates derived using predictive tidal charts produce overall higher uplift estimates in comparison to tide-gauge calibrated and instrumental methods, with mean uplift results 0.21 m or 20% higher than LiDAR results. This low-tech methodology can, however, produce uplift results that are broadly consistent with instrumental methodologies and might be applied with confidence in remote locations where satellite data or local tide-gauge measurements are not available.

AGUFM, Dec 1, 2018

Subduction systems globally terminate, allowing plate-motion to be transferred from the oceanic m... more Subduction systems globally terminate, allowing plate-motion to be transferred from the oceanic megathrust onto continental and/or oceanic transform faults. The mechanism of this kinematic transition over earthquake timescales is, however, poorly understood due to a lack of relevant data. Here, we study the 2016 M w 7.8 Kaikōura Earthquake in New Zealand, the first large instrumentally-recorded earthquake across a subduction-termination, to investigate this transfer mechanism in detail. We find that the Kaikōura Earthquake, unlike standard subduction earthquakes globally, involved a predominance (∼80%) of coseismic-slip on upper-plate faults and minor triggered-slip on the underlying oceanic subduction-thrust. In the months following the earthquake, the subduction-thrust accommodated most of the earthquake's afterslip down-dip of its co-seismic rupture zone. This top-down strain-release mechanism is in accord with local geological, geodetic and historical seismicity data which suggest that the bulk of plate-convergence (>75%) is accommodated in the upper-plate. We suggest, therefore, that this alternative strain-release mechanism, which is distinct from standard plate-boundary earthquakes, is characteristic of subduction-terminations and results in the majority of seismic/tsunami hazard being on steep near-surface faults.

EGU General Assembly Conference Abstracts, Apr 1, 2018

The 2016 M7.8 Kaikōura Earthquake triggered global scientific interest. This is because this eart... more The 2016 M7.8 Kaikōura Earthquake triggered global scientific interest. This is because this earthquake ruptured multiple faults (n>20), mainly onshore, and across an active subduction margin providing, thus, a unique opportunity to examine co-seismic fault interactions between various elements of a subduction system. Although to date, numerous studies have modeled this earthquake, it is still unclear whether or not the plate-interface was involved and if so, to what extent. Here we use published and new (this study) field measurements of uplifted marine biota together with displacements recorded by LiDAR, GPS, seismographs and tide-gauges to chart coseismic deformation patterns in the broader Kaikōura region and model the major seismic sources involved in this event. Our analysis captures a rare snapshot of slip-transfer between upper-plate faults and the plate-interface. Despite its apparent involvement in the Kaikōura Earthquake, the plate-interface moved with a mean slip of only 0.6 m. This is because a significant amount of convergent-related slip was accommodated by a thrust fault that splays off the plate-interface and extends within the upper crust. The Kaikōura earthquake suggests that these large splay-thrust faults provide a key mechanism in the transfer of plate motion at the termination of a subduction margin and represent an important seismic/tsunami hazard.

Earth and Planetary Science Letters, 2017

The M7.8 Kaikoura Earthquake that struck the northeastern South Island, New Zealand, on November ... more The M7.8 Kaikoura Earthquake that struck the northeastern South Island, New Zealand, on November 14, 2016 (local time), is one of the largest ever instrumentally recorded earthquakes in New Zealand. It occurred at the southern termination of the Hikurangi subduction margin, where the subducting Pacific Plate transitions into the dextral Alpine transform fault. The earthquake produced significant distributed uplift along the northeastern part of the South Island, reaching a peak amplitude of ∼8 m, which was accompanied by large (≥10 m) horizontal coseismic displacements at the ground surface along discrete active faults. The seismic waveforms' expression of the main shock indicate a complex rupture process. Early automated centroid moment tensor solutions indicated a strong non-double-couple term, which supports a complex rupture involving multiple faults. The hypocentral distribution of aftershocks, which appears diffuse over a broad region, clusters spatially along lineaments with different orientations. A key question of global interest is to shed light on the mechanism with which such a complex rupture occurred, and whether the underlying plate-interface was involved in the rupture. The consequences for seismic hazard of such a distributed, shallow faulting is important to be assessed. We perform a broad seismological analysis, combining regional and teleseismic seismograms, GPS and InSAR, to determine the rupture process of the main shock and moment tensors of 118 aftershocks down to Mw 4.2. The joint interpretation of the main rupture and aftershock sequence allow reconstruction of the geometry, and suggests sequential activation and slip distribution on at least three major active fault domains. We find that the rupture nucleated as a weak strike-slip event along the Humps Fault, which progressively propagated northward onto a shallow reverse fault, where most of the seismic moment was released, before it triggered slip on a second set of strike-slip faults at the northern end of the rupture. The northern and southern strike-slip fault domains have the same orientation but are spatially separated by >15 km. In our model, the low angle splay thrust fault is located above the slab and connects the strike-slip faults kinematically. During the aftershock phase, the entire fault system remained active.

Bulletin of the Geological Society of Greece, 2017

The Rare Earth Elements and Yttrium (REE-Y) have recently been proposed as good proxies for ident... more The Rare Earth Elements and Yttrium (REE-Y) have recently been proposed as good proxies for identifying rupture zones on carbonate fault scarps. Indeed, fluctuations in the REE-Y concentrations along a fault plane may be linked to the number and size of earthquakes that ruptured the fault. The enrichment is attributed to the contact of the soil with the carbonate fault scarp. Our study presents preliminary results from a series of experiments that aim to shed light on the mechanism associated with the REE-Y sorption on the limestone-soil interface. Rain simulation pot experiments, kinetic and isotherm batch experiments were employed to describe the mechanism of REE-Y sorption in calcite. Results reveal fast REE-Y sorption on the limestone surface after the simulation of five years of rainfall. The fast REE-Y sorption is also supported by the kinetic experiments. Isotherm tests show the higher affinity of calcite in the Light Rare Earth (LREE) compared to the Heavy Rare Earth Element...

Annals of Geophysics, 2009

The El Camp Fault (Catalan Coastal Ranges, NE Iberian Peninsula) is a slow slipping normal fault ... more The El Camp Fault (Catalan Coastal Ranges, NE Iberian Peninsula) is a slow slipping normal fault whose seismic potential has only recently been recognised. New geomorphic and trench investigations were carried out during a training course across the El Camp Fault at the La Porquerola alluvial fan site. A new trench (trench 8) was dug close to a trench made previously at this site (trench 4). With the aid of two long topographic profiles across the fault scarp we obtained a vertical slip rate ranging between 0.05 and 0.08 mm/yr. At the trench site, two main faults, which can be correlated between trenches 8 and 4, make up the fault zone. Using trench analysis three paleoseismic events were identified, two between 34. 000 and 125. 000 years BP (events 3 and 2) and another event younger than 13 500 years BP (event 1), which can be correlated, respectively, with events X (50. 000-125.000 years BP), Y (35.000-50. 000 years BP) and Z (3000-25.000 years BP). The last seismic event at the La Porquerola alluvial fan site is described for the first time, but with some uncertainties.

HNPS Advances in Nuclear Physics, Dec 13, 2022

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0.

faults: An alternative model from

<p>As well as slip on a primary fault plane, earthquakes can produce slip on neighb... more <p>As well as slip on a primary fault plane, earthquakes can produce slip on neighbouring faults which are not directly linked to the main source. This slip is called syn-seismic. With modern space-borne observation techniques, we observe syn-seismic slip down to a few centimeters on active faults nearby the source. An excellent example is the mapped slip on secondary faults during the 2019 Ridgecrest earthquake sequence in California. The overall spatial pattern of syn-seismic slip with respect to the main fault suggest that these faults respond to local stress changes caused by the main shock.</p> <p>Data that enable the detection of surface fault slip on such small scale are provided by optical and radar satellites which allow a very high precision with high spatial resolution. In particular, short revisit times of these satellite observations lead to high coherence between images matched in pixel-offset and radar interferometric techniques.</p> <p>We present further examples of syn-seismic fault slip during ~M6 earthquakes from different regions, such as those recorded in Greece in 2021 (Tyrnavos and Arkalochori) and 2020 in Tibet (W Xizang and near Xegar). We use Sentinel-1 interferometric wide-swath SAR acquisitions, which we process on the highest spatial resolution and apply weak filtering only. Our examples have in common that their syn-seismic fault activation reveals slip of a few centimeters only, persistently along a section of the fault’s length. The slip directions commonly appear to follow the coseismic surface displacement gradients which, in some cases, results in reverse slip on long-term normal faults. The activated faults were either faults previously mapped or concealed faults which were identified due to InSAR.</p> <p>It is difficult to estimate the depth of syn-seismic fault slip and therefore how much strain has been released due to localized stress changes. We are also uncertain of the extent to which this small slip release contributes to the long-term displacement and displacement rate on faults and whether its contribution should be included in dislocation fault slip models. Our compilation suggests that syn-seismic slip is rather common, despite the rarity of previous observations, and is now detectable only because of improved resolution provided by InSAR data.</p>

Copernicus GmbH, Jan 28, 2017

Copernicus GmbH, Feb 18, 2017

EGU General Assembly Conference Abstracts, Apr 1, 2019

Geophysical Journal International, Nov 25, 2020

Clusty is a new open source toolbox dedicated to earthquake clustering based on waveforms recorde... more Clusty is a new open source toolbox dedicated to earthquake clustering based on waveforms recorded across a network of seismic stations. Its main application is the study of active faults and the detection and characterization of faults and fault networks. By using a density-based clustering approach, earthquakes pertaining to a common fault can be recognized even over long fault segments, and the first-order geometry and extent of active faults can be inferred. Clusty implements multiple techniques to compute a waveform based network similarity from maximum cross-correlation coefficients at multiple stations. The clustering procedure is designed to be transparent and parameters can be easily tuned. It is supported by a number of analysis visualization tools which help to assess the homogeneity within each cluster and the differences among distinct clusters. The toolbox returns graphical representations of the results. A list of representative events and stacked waveforms facilitate further analyses like moment tensor inversion. Results obtained in various frequency bands can be combined to account for large magnitude ranges. Thanks to the simple configuration, the toolbox is easily adaptable to new data sets and to large magnitude ranges. To show the potential of our new toolbox, we apply Clusty to the aftershock sequence of the M w 6.9 25 October 2018 Zakynthos (Greece) Earthquake. Thanks to the complex tectonic setting at the western termination of the Hellenic Subduction System where multiple faults and faulting styles operate simultaneously, the Zakynthos data set provides an ideal case-study for our clustering analysis toolbox. Our results support the activation of several faults and provide insight into the geometry of faults or fault segments. We identify two large thrust faulting clusters in the vicinity of the main shock and multiple strike-slip clusters to the east, west and south of these clusters. Despite its location within the largest thrust cluster, the main shock does not show a high waveform similarity to any of the clusters. This is consistent with the results of other studies suggesting a complex failure mechanism for the main shock. We propose the existence of conjugated strikeslip faults in the south of the study area. Our waveform similarity based clustering toolbox is able to reveal distinct event clusters which cannot be discriminated based on locations and/or timing only. Additionally, the clustering results allows distinction between fault and auxiliary planes of focal mechanisms and to associate them to known active faults.

Journal Of Geophysical Research: Solid Earth, 2017

In this study we utilize regional and teleseismic earthquake moment tensor solutions in order to ... more In this study we utilize regional and teleseismic earthquake moment tensor solutions in order to infer the contemporary crustal stress in the Greek region. We focus on crustal earthquakes and select only solutions with good waveform fits and well-resolved nodal planes. A data set of 1614 focal mechanisms is used as input to a regional-scale damped stress inversion algorithm over a grid whose node spacing is 0.35°. Several resolution and sensitivity tests are performed in order to ascertain the robustness of our results. Our findings show that for most of the Greek region the largest principal stress σ 1 is vertically oriented and that the minimum principal stress axis σ 3 are subhorizontal with a predominant N-S orientation. In the SW Peloponnese the orientation of σ 3 axes rotates clockwise and in SE Aegean counterclockwise. These results are in agreement with the generally accepted model that slab rollback combined with gravitational spreading of the Aegean lithosphere are the main causes of the extension. Transitions between different faulting types in NW Greece or in the Aegean occur within narrow zones in the order of tens of kilometers. A visual comparison of the principal horizontal stress axes and the principal strain axes derived from GPS observations shows good agreement, suggesting that the crust in the Greek region behaves largely in an elastic manner.

EGU General Assembly Conference Abstracts, Apr 1, 2019

The 2016 M w 7.8 Kaikōura Earthquake (South Island, New Zealand) caused widespread complex ground... more The 2016 M w 7.8 Kaikōura Earthquake (South Island, New Zealand) caused widespread complex ground deformation including significant coastal uplift of rocky shorelines. This coastal deformation is used here to develop a new methodology, in which intertidal marine biota have been calibrated against tide-gauge records to quantitatively constrain predeformation biota living depths relative to sea level. This living depth is then applied to biologically measured tectonic uplift at three other locations along the Kaikōura coast. We also test how tectonic uplift measured using this calibrated marine biota compares to vertical deformation measured, at the same localities, using instrumental methods [Light Detection and Ranging (LiDAR) and strong motion data], and non-calibrated biological methods. Data show that where biological data is collected by RTK-GNSS in sheltered locations, this new tide-gauge calibration method estimates tectonic uplift with an accuracy of +/-≤0.07 m in the vicinity of the tide-gauge, and an overall mean accuracy of +/-0.10 m or 10% compared to differential LiDAR methods for all locations. Sites exposed to high wave wash, or data collected by tape-measure, are more likely to show higher uplift results. Tectonic uplift estimates derived using predictive tidal charts produce overall higher uplift estimates in comparison to tide-gauge calibrated and instrumental methods, with mean uplift results 0.21 m or 20% higher than LiDAR results. This low-tech methodology can, however, produce uplift results that are broadly consistent with instrumental methodologies and might be applied with confidence in remote locations where satellite data or local tide-gauge measurements are not available.

AGUFM, Dec 1, 2018

Subduction systems globally terminate, allowing plate-motion to be transferred from the oceanic m... more Subduction systems globally terminate, allowing plate-motion to be transferred from the oceanic megathrust onto continental and/or oceanic transform faults. The mechanism of this kinematic transition over earthquake timescales is, however, poorly understood due to a lack of relevant data. Here, we study the 2016 M w 7.8 Kaikōura Earthquake in New Zealand, the first large instrumentally-recorded earthquake across a subduction-termination, to investigate this transfer mechanism in detail. We find that the Kaikōura Earthquake, unlike standard subduction earthquakes globally, involved a predominance (∼80%) of coseismic-slip on upper-plate faults and minor triggered-slip on the underlying oceanic subduction-thrust. In the months following the earthquake, the subduction-thrust accommodated most of the earthquake's afterslip down-dip of its co-seismic rupture zone. This top-down strain-release mechanism is in accord with local geological, geodetic and historical seismicity data which suggest that the bulk of plate-convergence (>75%) is accommodated in the upper-plate. We suggest, therefore, that this alternative strain-release mechanism, which is distinct from standard plate-boundary earthquakes, is characteristic of subduction-terminations and results in the majority of seismic/tsunami hazard being on steep near-surface faults.

EGU General Assembly Conference Abstracts, Apr 1, 2018

The 2016 M7.8 Kaikōura Earthquake triggered global scientific interest. This is because this eart... more The 2016 M7.8 Kaikōura Earthquake triggered global scientific interest. This is because this earthquake ruptured multiple faults (n>20), mainly onshore, and across an active subduction margin providing, thus, a unique opportunity to examine co-seismic fault interactions between various elements of a subduction system. Although to date, numerous studies have modeled this earthquake, it is still unclear whether or not the plate-interface was involved and if so, to what extent. Here we use published and new (this study) field measurements of uplifted marine biota together with displacements recorded by LiDAR, GPS, seismographs and tide-gauges to chart coseismic deformation patterns in the broader Kaikōura region and model the major seismic sources involved in this event. Our analysis captures a rare snapshot of slip-transfer between upper-plate faults and the plate-interface. Despite its apparent involvement in the Kaikōura Earthquake, the plate-interface moved with a mean slip of only 0.6 m. This is because a significant amount of convergent-related slip was accommodated by a thrust fault that splays off the plate-interface and extends within the upper crust. The Kaikōura earthquake suggests that these large splay-thrust faults provide a key mechanism in the transfer of plate motion at the termination of a subduction margin and represent an important seismic/tsunami hazard.

Earth and Planetary Science Letters, 2017

The M7.8 Kaikoura Earthquake that struck the northeastern South Island, New Zealand, on November ... more The M7.8 Kaikoura Earthquake that struck the northeastern South Island, New Zealand, on November 14, 2016 (local time), is one of the largest ever instrumentally recorded earthquakes in New Zealand. It occurred at the southern termination of the Hikurangi subduction margin, where the subducting Pacific Plate transitions into the dextral Alpine transform fault. The earthquake produced significant distributed uplift along the northeastern part of the South Island, reaching a peak amplitude of ∼8 m, which was accompanied by large (≥10 m) horizontal coseismic displacements at the ground surface along discrete active faults. The seismic waveforms' expression of the main shock indicate a complex rupture process. Early automated centroid moment tensor solutions indicated a strong non-double-couple term, which supports a complex rupture involving multiple faults. The hypocentral distribution of aftershocks, which appears diffuse over a broad region, clusters spatially along lineaments with different orientations. A key question of global interest is to shed light on the mechanism with which such a complex rupture occurred, and whether the underlying plate-interface was involved in the rupture. The consequences for seismic hazard of such a distributed, shallow faulting is important to be assessed. We perform a broad seismological analysis, combining regional and teleseismic seismograms, GPS and InSAR, to determine the rupture process of the main shock and moment tensors of 118 aftershocks down to Mw 4.2. The joint interpretation of the main rupture and aftershock sequence allow reconstruction of the geometry, and suggests sequential activation and slip distribution on at least three major active fault domains. We find that the rupture nucleated as a weak strike-slip event along the Humps Fault, which progressively propagated northward onto a shallow reverse fault, where most of the seismic moment was released, before it triggered slip on a second set of strike-slip faults at the northern end of the rupture. The northern and southern strike-slip fault domains have the same orientation but are spatially separated by >15 km. In our model, the low angle splay thrust fault is located above the slab and connects the strike-slip faults kinematically. During the aftershock phase, the entire fault system remained active.

Bulletin of the Geological Society of Greece, 2017

The Rare Earth Elements and Yttrium (REE-Y) have recently been proposed as good proxies for ident... more The Rare Earth Elements and Yttrium (REE-Y) have recently been proposed as good proxies for identifying rupture zones on carbonate fault scarps. Indeed, fluctuations in the REE-Y concentrations along a fault plane may be linked to the number and size of earthquakes that ruptured the fault. The enrichment is attributed to the contact of the soil with the carbonate fault scarp. Our study presents preliminary results from a series of experiments that aim to shed light on the mechanism associated with the REE-Y sorption on the limestone-soil interface. Rain simulation pot experiments, kinetic and isotherm batch experiments were employed to describe the mechanism of REE-Y sorption in calcite. Results reveal fast REE-Y sorption on the limestone surface after the simulation of five years of rainfall. The fast REE-Y sorption is also supported by the kinetic experiments. Isotherm tests show the higher affinity of calcite in the Light Rare Earth (LREE) compared to the Heavy Rare Earth Element...

Annals of Geophysics, 2009

The El Camp Fault (Catalan Coastal Ranges, NE Iberian Peninsula) is a slow slipping normal fault ... more The El Camp Fault (Catalan Coastal Ranges, NE Iberian Peninsula) is a slow slipping normal fault whose seismic potential has only recently been recognised. New geomorphic and trench investigations were carried out during a training course across the El Camp Fault at the La Porquerola alluvial fan site. A new trench (trench 8) was dug close to a trench made previously at this site (trench 4). With the aid of two long topographic profiles across the fault scarp we obtained a vertical slip rate ranging between 0.05 and 0.08 mm/yr. At the trench site, two main faults, which can be correlated between trenches 8 and 4, make up the fault zone. Using trench analysis three paleoseismic events were identified, two between 34. 000 and 125. 000 years BP (events 3 and 2) and another event younger than 13 500 years BP (event 1), which can be correlated, respectively, with events X (50. 000-125.000 years BP), Y (35.000-50. 000 years BP) and Z (3000-25.000 years BP). The last seismic event at the La Porquerola alluvial fan site is described for the first time, but with some uncertainties.

HNPS Advances in Nuclear Physics, Dec 13, 2022

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0.

faults: An alternative model from

<p>As well as slip on a primary fault plane, earthquakes can produce slip on neighb... more <p>As well as slip on a primary fault plane, earthquakes can produce slip on neighbouring faults which are not directly linked to the main source. This slip is called syn-seismic. With modern space-borne observation techniques, we observe syn-seismic slip down to a few centimeters on active faults nearby the source. An excellent example is the mapped slip on secondary faults during the 2019 Ridgecrest earthquake sequence in California. The overall spatial pattern of syn-seismic slip with respect to the main fault suggest that these faults respond to local stress changes caused by the main shock.</p> <p>Data that enable the detection of surface fault slip on such small scale are provided by optical and radar satellites which allow a very high precision with high spatial resolution. In particular, short revisit times of these satellite observations lead to high coherence between images matched in pixel-offset and radar interferometric techniques.</p> <p>We present further examples of syn-seismic fault slip during ~M6 earthquakes from different regions, such as those recorded in Greece in 2021 (Tyrnavos and Arkalochori) and 2020 in Tibet (W Xizang and near Xegar). We use Sentinel-1 interferometric wide-swath SAR acquisitions, which we process on the highest spatial resolution and apply weak filtering only. Our examples have in common that their syn-seismic fault activation reveals slip of a few centimeters only, persistently along a section of the fault’s length. The slip directions commonly appear to follow the coseismic surface displacement gradients which, in some cases, results in reverse slip on long-term normal faults. The activated faults were either faults previously mapped or concealed faults which were identified due to InSAR.</p> <p>It is difficult to estimate the depth of syn-seismic fault slip and therefore how much strain has been released due to localized stress changes. We are also uncertain of the extent to which this small slip release contributes to the long-term displacement and displacement rate on faults and whether its contribution should be included in dislocation fault slip models. Our compilation suggests that syn-seismic slip is rather common, despite the rarity of previous observations, and is now detectable only because of improved resolution provided by InSAR data.</p>

Copernicus GmbH, Jan 28, 2017

Copernicus GmbH, Feb 18, 2017

EGU General Assembly Conference Abstracts, Apr 1, 2019