Victor Mocanu - Academia.edu (original) (raw)

Papers by Victor Mocanu

We present a teleseismic travel-time inversion for upper-mantle velocity structure beneath the Ch... more We present a teleseismic travel-time inversion for upper-mantle velocity structure beneath the Chile triple junction region. Data were recorded at 46 seismic stations deployed in southern Chile from December 2004 to February 2007 (for details, see the Chile Ridge Subduction Project, http://seismology.geology.ufl.edu/chile). The area covered by the network (42-46 degrees South and 72-78 degrees West) lies above the projected position of the subducted Chile ridge, which separates the Nazca and Antarctic oceanic plates. Because the Nazca plate subducts nearly 5 cm/yr faster than the Antarctic plate, the trailing edge of the last Nazca lithosphere formed before the ridge subducts has been inferred to separate steadily from the leading edge of the Antarctic lithosphere, forming progressively larger slab windows with depth. The relative delay times are obtained via a multi-channel cross correlation of band-passed waveforms for each teleseismic event. These data are then inverted using an iterative, robust, non-linear scheme, which parameterizes the 3-D velocity variations as splines under tension constrained at over 30,000 nodes beneath the region.. We image a high-velocity slab in the upper mantle dipping steeply to the East, which we associate with the subducted Nazca oceanic lithosphere, and a distinct low-velocity anomaly at the projected location of the subducted Chile ridge.

In this study we analyse data recorded at the densely spaced Chile Ridge Subduction Project (CRSP... more In this study we analyse data recorded at the densely spaced Chile Ridge Subduction Project (CRSP) stations, to image fundamental mode Rayleigh wavefronts as they pass through the region. The processing involves first cleaning the seismograms by means of frequency time analysis (FTAN), whereby we test different filtering techniques, and cross-correlating the seismograms at a series of frequencies. Wavefronts are fit to the relative arrival times with a least squares fitting procedure. Our results show that the shape of the wavefronts change within the study region and that for certain events, particularly those with wavepaths that follow the west coast line of South America, wavefronts are not perpendicular to the great circle path between the source and the receiver. We discuss the implications of this discrepancy and interpret the frequency dependent wavefront modulations in terms of interstation velocity structure. Additionally, we combine the dispersion curves obtained during the FTAN with existing data to present an updated tomographic model of the whole South American continent. This marks a step forward from existing models, which typically suffer from poor data coverage in the southernmost parts of continental South America.

Journal of Seismology, 2010

A seismic swarm at the Aysén fjord started in January, 2007, reaching its highest activity betwee... more A seismic swarm at the Aysén fjord started in January, 2007, reaching its highest activity between January and April, 2007. It was punctuated by the Mw5.3 23rd January event and the Mw6.2 21st April event which triggered a water-wave due to massive landslides; both with dextral strike slip focal mechanisms. More than 100 events were relocated with the Joint Hypocenter Determination method to study the depth distribution of the events of the swarm recorded by the Chile Ridge Subduction Project local network. The events are associated to a small area of approximately 7 × 7 km located in the Aysén fjord, on one of the main branches of the Liquiñe–Ofqui fault. Distribution in depth is located between 0 and 8 km and presents a west high dip with almost NS strike, consistent with the main trending of the Liquiñe–Ofqui fault and the published focal mechanisms. These characteristics, among others, suggest that the Liquiñe–Ofqui fault is active in this region and thus seismic risk has to be re-determined.

We analyse data recorded at stations of the densely spaced Chile Ridge Subduction Project (CRSP),... more We analyse data recorded at stations of the densely spaced Chile Ridge Subduction Project (CRSP), to map phase velocity variations within the array region. We map phase velocity in a two step procedure: first, we take advantage of the high station density of CRSP and thus similar waveforms recorded at the seismometers by cross-correlating filtered seismograms to obtain relative arrival times of fundamental mode Rayleigh waves at different periods ranging from 20 to 100 seconds. We then fit wave fronts to these arrival times as they traverse the array. Typically these wave fronts are nearly but not entirely plane and perpendicular to the great circle path as they enter the array, which indicates heterogeneity outside of CRSP. Changes in the wave fronts as they pass through the region indicate heterogeneity beneath the array. In the second step we further investigate these heterogeneities and image the mantle beneath CRSP by inverting the relative arrival times for phase velocities within the array.

Making use of teleseismic data recorded at 46 seismic stations deployed in southern Chile from De... more Making use of teleseismic data recorded at 46 seismic stations deployed in southern Chile from December 2004 to February 2007 (see the Chile Ridge Subduction Project; http:seismology.geology.ufl.edu/chile), we present a preliminary inversion for the mantle P-wave velocity structure beneath the region. The area covered by the network (42-46 degrees South and 72-78 degrees West) lies above the projected position of the subducted Chile ridge, which separates the Nazca and Antarctic oceanic plates. Because the Nazca plate subducts nearly 5 cm/yr faster than the Antarctic plate, the trailing edge of the last Nazca lithosphere formed before the ridge subducts has been inferred to separate steadily from the leading edge of the Antarctic lithosphere, forming progressively larger slab windows with depth. We use the teleseismic inversion to test models for such slab windows. The P-wave relative delay times are obtained via a multi-channel cross correlation of band-passed waveforms for each teleseismic event. These data are then inverted using an iterative, robust, non-linear scheme which parameterizes the 3-D velocity variations as splines under tension constrained at over 30,000 nodes beneath the region.

Project DRACULA (Deep Reflection Acquisition Constraining Unusual Lithospheric Activity), a colla... more Project DRACULA (Deep Reflection Acquisition Constraining Unusual Lithospheric Activity), a collaboration between the University of South Carolina, the University of Bucharest, and the National Institute for Earth Physics in Romania, involved the acquisition of 320 km of deep (60 s) multichannel seismic reflection data in the summer of 2004. Project DRACULA involved the acquisition of three transects (DRACULA I, II, and III) surrounding the Vrancea zone of Romania in order to evaluate the existing competing models for the origin, lithospheric structure, and geodynamic setting of this highly disputable intermediate-depth (70-200 km) seismogenic region. While the DRACULA I profile, acquired in the hinterland of the southeastern Carpathians, is presented elsewhere, here we discuss preliminary results from lines DRACULA II and III collected in the foreland, east and south of the seismogenic area. DRACULA II and III profiles were designated to image the crustal structure of the foreland across the Pecineaga-Camena, and respectively, Intramoesian Faults, two of the active foreland faults, in order to place constraints on the duration, timing, and scale of foreland deformation that appears to be a direct response to the Vrancea seismogenic body. The DRACULA II line shows strong subhorizontal reflections from 14.5-15.0 (approx. 45-48 km) in the eastern side of the Pecineaga-Camena fault that we interpret to be the Moho. Unusually layered reflectivity is seen down to 20 s in this part of the line. A very intriguing high-amplitude subhorizontal reflector, approximately 7 km long, is observed at 35.5 s (approx. 130 km). The western side of the line, across the fault, displays a fairly transparent lower crust and uppermost mantle, possibly indicating the depth penetration of the Pecineaga-Camena fault across the Moho. The DRACULA III line displays a very high amplitude reflection at 14.0 s (aprox. 42 km) in the south-west that dips slightly to 14.5-15.s (45-48 km) in the north-east. This reflection is interpreted to be the Moho, but it is premature to comment whether this variation in its depth is related to the penetration of the Intramoesian fault into the lithospheric mantle. Although preliminary, results from the DRACULA II and III profiles indicate that the active crustal faults in the foreland that have significant surface expressions (up to 100 m escarpments) continue in the uppermost mantle, and may be related to the Vrancea seismogenic zone.

The seismic refraction project VRANCEA2001, which was carried out during August - September 2001,... more The seismic refraction project VRANCEA2001, which was carried out during August - September 2001, is the second profile performed in southeastern Romania to study the crustal and uppermost mantle structure underneath the Vrancea epicentral region in the southeastern Carpathians. Both projects are a contribution to the joint German-Romanian research programme "Strong earthquakes - a challenge for Geosciences and Civil Engineering" installed by the "Sonderforschungsbereich" 461 at the University of Karlsruhe, Germany, in collaboration with various research institutions in Romania. The seismic refraction investigation of sub-project A1, so far, comprises three lines: (1) a 300 km long line from the Danube river SW of the city of Giurgiu across Bucharest and on to the city of Bacau traversing the Vrancea epicentral region in SSW-NNE direction. (2) A 70 km long E-W directed fan line along the Putna valley north of the Vrancea epicentral region. (3) This new 460 km long NE-SW directed line from the Black Sea to the Transsylvanian Basin. Data acquisition took place, as part of the integrated refraction/reflection seismic field programme "VRANCEA-2001" co-ordinated at Karlsruhe University (cf. Abstract, Part 2). Along this new line (3) a total of 11 shot points were established, 10 on the main line with charges ranging from 300 kg to 1500 kg and an average shot point spacing of 40 km. For the last shot point our Hungarian colleagues re-occupied one of the CELEBRATION2000 shot points. A total of 460 recording stations were deployed with an average spacing of 1 km. Of those, 150 stations were 3-component stations of type PDAS-100 and REFTEK and provided by the GeoForschungsZentrum in Potsdam, Germany. The rest were small 1-component stations (Type "Texans" from Reftek) and provided by UTEP and IRIS/PASSCAL. The detailed investigation of the crust and upper mantle of both projects aims to contribute to a better understanding of the causes for the occurrence of intermediate depth earthquakes in the Vrancea epicentral region and their relationship to the subduction model. In this contribution we will present the project and some first data examples.

Eos, Transactions American Geophysical Union, 2004

The Vrancea region in the South-East Carpathians of Romania is a seismically active area related ... more The Vrancea region in the South-East Carpathians of Romania is a seismically active area related to past or ongoing lithosphere subduction. One of the outstanding questions is whether the subducting slab is attached, detached or in the process of being detached from the overlying lithosphere. GPS campaigns of 3-D crustal displacements in this region, performed by ISES (Netherlands) in collaboration with SFB-461 (Germany) and the University of Bucharest (Romania), are expected to assist in solving this issue. Measurements have been performed in this area since 1995 and the current GPS network consists of more than 50 campaign points and six permanent GPS stations. However, ongoing deformation related to large (Mw > 7) earthquakes that struck the Vrancea region in 1977, 1986 and 1990 could have a considerable contribution to GPS-observed displacement rates. This so-called postseismic deformation results from viscoelastic relaxation of crustal and shallow upper-mantle low-viscosity zones due to the redistributed stress and strain after faulting. Results from the GPS campaigns combined with numerical postseismic deformation modelling indicate that postseismic relaxation is even the dominant mechanism for present-day horizontal crustal displacements in the Vrancea region. This suggests small (< 1 - 2 mm/yr) to insignificant ongoing plate convergence. Vector solution directions are not very sensitive to the earth model, while magnitudes agree for a seismically and tectonically consistent earth model for the Vrancea region. This has important implications for interpreting neotectonic processes in the Carpathians.

Geophysical Journal International, 2011

We relocated the six large-magnitude (5.2 < Mw < 6.2) earthquakes of the destructive, tsunamigeni... more We relocated the six large-magnitude (5.2 < Mw < 6.2) earthquakes of the destructive, tsunamigenic Aysen seismic swarm, which occurred from 2007 January-October in Patagonian Chile. We used P and SH arrival times from near-source stations of a temporary seismic network fortuitously deployed in the area when the swarm began, and also traveltimes to stations of the permanent global networks, to locate the 2007 January 23, Mw 5.2 earthquake, the first of the six large magnitude events. This earthquake's hypocentre lies at shallow depth (<10 km) on the eastern strand of a major intraarc shear zone, the dextral Liquiñe-Ofqui fault zone. Using the hypocentre of the January 23 earthquake as a fixed location, we relocated the five other large magnitude Aysen earthquakes by joint hypocentral determination. Four of these five events also occurred at shallow depth on the eastern strand Liquiñe-Ofqui fault, whereas the 2007 April 2, earthquake occurred some 45 km to the west on the Aysen fault, a strike-slip duplex fault that segments the area between the eastern and western Liquiñe-Ofqui fault strands. The five earthquakes on the Liquiñe-Ofqui fault were all produced by dextral slip on ˜N-S nodal planes approximately parallel to the mapped trace of the fault. The April 2 earthquake resulted from normal slip on the Aysen fault. Modelling of Coulomb stress changes on the nodal planes of the April 2 earthquake shows that the cumulative slip on the Liquiñe-Ofqui fault strand could have triggered the April 2 earthquake. Similarly, the April 2 earthquake may have triggered the Mw 6.2 April 21 earthquake, which caused mass wasting into Aysen Fjord, generating a destructive tsunami. The system of channels and fjords in the study region is a major shipping route around South America, and therefore careful evaluation of the seismic hazard is warranted.

Eos, Transactions American Geophysical Union, 1998

Geophysical experiments next year in Romania may provide insight into a common but short-lived se... more Geophysical experiments next year in Romania may provide insight into a common but short-lived seismic process that can be observed and understood at only one spot on Earth at present. About 150 stations will be set up in the Vrancea area in the southeast Carpathian Mountains to, in effect, record the terminal phase of the detachment of a subducting slab of oceanic lithosphere. This is a major regional tomographic study using a large number of broadband seismometers, which will operate for 6 months. Images will be used for hazard assessment as well as for a delineation of detachment history.Active subduction of oceanic lithosphere at convergent plate boundaries involves earthquakes, magmatism, metamorphism, and deformation—some of the most vivid manifestations of any plate tectonic process. The initiation and termination of subduction, however, remains relatively poorly understood. When convergence of lithospheric plates ceases and the suction force of the subducting plate becomes negligible, the subducting slab moves into an almost vertical position. If subduction occurs in an arcuate geometry, the slab is likely to be segmented.

More than half of the Earth's population lives within the confines of the Tethyan tectonic collis... more More than half of the Earth's population lives within the confines of the Tethyan tectonic collision belt (Figure 1), a high-risk zone that contains at least 20 of the world's “mega-cities.” During the 20th century alone, collision-related seismicity and explosive volcanism (Figure 2) caused over a million deaths and catastrophic economic losses in this region. Destructive volcanism results mostly from the eruption of viscous, volatile-rich magma generated near converging or colliding plate margins, while the most damaging earthquakes are produced by post-collision tectonic thrusting and strike-slip faulting. An exploratory program has been initiated to coordinate research in the Tethyan region, appraise the role of collision-related mantle-dynamics in seismicity and volcanism, and assess their potential significance in mitigating seismic and volcanic hazards across the entire Tethyan belt.

Gsa Today, 2010

... Cande et al., 1987; Bangs et al., 1992; Lagabrielle et al., 2004; Ranero et al., 2006), as we... more ... Cande et al., 1987; Bangs et al., 1992; Lagabrielle et al., 2004; Ranero et al., 2006), as well as important differences between structures, morphology, and evolution in foreland areas north and south, and backarc areas well east of the present triple junction (Ramos, 1989; Flint ...

We present a teleseismic travel-time inversion for upper-mantle velocity structure beneath the Ch... more We present a teleseismic travel-time inversion for upper-mantle velocity structure beneath the Chile triple junction region. Data were recorded at 46 seismic stations deployed in southern Chile from December 2004 to February 2007 (for details, see the Chile Ridge Subduction Project, http://seismology.geology.ufl.edu/chile). The area covered by the network (42-46 degrees South and 72-78 degrees West) lies above the projected position of the subducted Chile ridge, which separates the Nazca and Antarctic oceanic plates. Because the Nazca plate subducts nearly 5 cm/yr faster than the Antarctic plate, the trailing edge of the last Nazca lithosphere formed before the ridge subducts has been inferred to separate steadily from the leading edge of the Antarctic lithosphere, forming progressively larger slab windows with depth. The relative delay times are obtained via a multi-channel cross correlation of band-passed waveforms for each teleseismic event. These data are then inverted using an iterative, robust, non-linear scheme, which parameterizes the 3-D velocity variations as splines under tension constrained at over 30,000 nodes beneath the region.. We image a high-velocity slab in the upper mantle dipping steeply to the East, which we associate with the subducted Nazca oceanic lithosphere, and a distinct low-velocity anomaly at the projected location of the subducted Chile ridge.

In this study we analyse data recorded at the densely spaced Chile Ridge Subduction Project (CRSP... more In this study we analyse data recorded at the densely spaced Chile Ridge Subduction Project (CRSP) stations, to image fundamental mode Rayleigh wavefronts as they pass through the region. The processing involves first cleaning the seismograms by means of frequency time analysis (FTAN), whereby we test different filtering techniques, and cross-correlating the seismograms at a series of frequencies. Wavefronts are fit to the relative arrival times with a least squares fitting procedure. Our results show that the shape of the wavefronts change within the study region and that for certain events, particularly those with wavepaths that follow the west coast line of South America, wavefronts are not perpendicular to the great circle path between the source and the receiver. We discuss the implications of this discrepancy and interpret the frequency dependent wavefront modulations in terms of interstation velocity structure. Additionally, we combine the dispersion curves obtained during the FTAN with existing data to present an updated tomographic model of the whole South American continent. This marks a step forward from existing models, which typically suffer from poor data coverage in the southernmost parts of continental South America.

Journal of Seismology, 2010

A seismic swarm at the Aysén fjord started in January, 2007, reaching its highest activity betwee... more A seismic swarm at the Aysén fjord started in January, 2007, reaching its highest activity between January and April, 2007. It was punctuated by the Mw5.3 23rd January event and the Mw6.2 21st April event which triggered a water-wave due to massive landslides; both with dextral strike slip focal mechanisms. More than 100 events were relocated with the Joint Hypocenter Determination method to study the depth distribution of the events of the swarm recorded by the Chile Ridge Subduction Project local network. The events are associated to a small area of approximately 7 × 7 km located in the Aysén fjord, on one of the main branches of the Liquiñe–Ofqui fault. Distribution in depth is located between 0 and 8 km and presents a west high dip with almost NS strike, consistent with the main trending of the Liquiñe–Ofqui fault and the published focal mechanisms. These characteristics, among others, suggest that the Liquiñe–Ofqui fault is active in this region and thus seismic risk has to be re-determined.

We analyse data recorded at stations of the densely spaced Chile Ridge Subduction Project (CRSP),... more We analyse data recorded at stations of the densely spaced Chile Ridge Subduction Project (CRSP), to map phase velocity variations within the array region. We map phase velocity in a two step procedure: first, we take advantage of the high station density of CRSP and thus similar waveforms recorded at the seismometers by cross-correlating filtered seismograms to obtain relative arrival times of fundamental mode Rayleigh waves at different periods ranging from 20 to 100 seconds. We then fit wave fronts to these arrival times as they traverse the array. Typically these wave fronts are nearly but not entirely plane and perpendicular to the great circle path as they enter the array, which indicates heterogeneity outside of CRSP. Changes in the wave fronts as they pass through the region indicate heterogeneity beneath the array. In the second step we further investigate these heterogeneities and image the mantle beneath CRSP by inverting the relative arrival times for phase velocities within the array.

Making use of teleseismic data recorded at 46 seismic stations deployed in southern Chile from De... more Making use of teleseismic data recorded at 46 seismic stations deployed in southern Chile from December 2004 to February 2007 (see the Chile Ridge Subduction Project; http:seismology.geology.ufl.edu/chile), we present a preliminary inversion for the mantle P-wave velocity structure beneath the region. The area covered by the network (42-46 degrees South and 72-78 degrees West) lies above the projected position of the subducted Chile ridge, which separates the Nazca and Antarctic oceanic plates. Because the Nazca plate subducts nearly 5 cm/yr faster than the Antarctic plate, the trailing edge of the last Nazca lithosphere formed before the ridge subducts has been inferred to separate steadily from the leading edge of the Antarctic lithosphere, forming progressively larger slab windows with depth. We use the teleseismic inversion to test models for such slab windows. The P-wave relative delay times are obtained via a multi-channel cross correlation of band-passed waveforms for each teleseismic event. These data are then inverted using an iterative, robust, non-linear scheme which parameterizes the 3-D velocity variations as splines under tension constrained at over 30,000 nodes beneath the region.

Project DRACULA (Deep Reflection Acquisition Constraining Unusual Lithospheric Activity), a colla... more Project DRACULA (Deep Reflection Acquisition Constraining Unusual Lithospheric Activity), a collaboration between the University of South Carolina, the University of Bucharest, and the National Institute for Earth Physics in Romania, involved the acquisition of 320 km of deep (60 s) multichannel seismic reflection data in the summer of 2004. Project DRACULA involved the acquisition of three transects (DRACULA I, II, and III) surrounding the Vrancea zone of Romania in order to evaluate the existing competing models for the origin, lithospheric structure, and geodynamic setting of this highly disputable intermediate-depth (70-200 km) seismogenic region. While the DRACULA I profile, acquired in the hinterland of the southeastern Carpathians, is presented elsewhere, here we discuss preliminary results from lines DRACULA II and III collected in the foreland, east and south of the seismogenic area. DRACULA II and III profiles were designated to image the crustal structure of the foreland across the Pecineaga-Camena, and respectively, Intramoesian Faults, two of the active foreland faults, in order to place constraints on the duration, timing, and scale of foreland deformation that appears to be a direct response to the Vrancea seismogenic body. The DRACULA II line shows strong subhorizontal reflections from 14.5-15.0 (approx. 45-48 km) in the eastern side of the Pecineaga-Camena fault that we interpret to be the Moho. Unusually layered reflectivity is seen down to 20 s in this part of the line. A very intriguing high-amplitude subhorizontal reflector, approximately 7 km long, is observed at 35.5 s (approx. 130 km). The western side of the line, across the fault, displays a fairly transparent lower crust and uppermost mantle, possibly indicating the depth penetration of the Pecineaga-Camena fault across the Moho. The DRACULA III line displays a very high amplitude reflection at 14.0 s (aprox. 42 km) in the south-west that dips slightly to 14.5-15.s (45-48 km) in the north-east. This reflection is interpreted to be the Moho, but it is premature to comment whether this variation in its depth is related to the penetration of the Intramoesian fault into the lithospheric mantle. Although preliminary, results from the DRACULA II and III profiles indicate that the active crustal faults in the foreland that have significant surface expressions (up to 100 m escarpments) continue in the uppermost mantle, and may be related to the Vrancea seismogenic zone.

The seismic refraction project VRANCEA2001, which was carried out during August - September 2001,... more The seismic refraction project VRANCEA2001, which was carried out during August - September 2001, is the second profile performed in southeastern Romania to study the crustal and uppermost mantle structure underneath the Vrancea epicentral region in the southeastern Carpathians. Both projects are a contribution to the joint German-Romanian research programme "Strong earthquakes - a challenge for Geosciences and Civil Engineering" installed by the "Sonderforschungsbereich" 461 at the University of Karlsruhe, Germany, in collaboration with various research institutions in Romania. The seismic refraction investigation of sub-project A1, so far, comprises three lines: (1) a 300 km long line from the Danube river SW of the city of Giurgiu across Bucharest and on to the city of Bacau traversing the Vrancea epicentral region in SSW-NNE direction. (2) A 70 km long E-W directed fan line along the Putna valley north of the Vrancea epicentral region. (3) This new 460 km long NE-SW directed line from the Black Sea to the Transsylvanian Basin. Data acquisition took place, as part of the integrated refraction/reflection seismic field programme "VRANCEA-2001" co-ordinated at Karlsruhe University (cf. Abstract, Part 2). Along this new line (3) a total of 11 shot points were established, 10 on the main line with charges ranging from 300 kg to 1500 kg and an average shot point spacing of 40 km. For the last shot point our Hungarian colleagues re-occupied one of the CELEBRATION2000 shot points. A total of 460 recording stations were deployed with an average spacing of 1 km. Of those, 150 stations were 3-component stations of type PDAS-100 and REFTEK and provided by the GeoForschungsZentrum in Potsdam, Germany. The rest were small 1-component stations (Type "Texans" from Reftek) and provided by UTEP and IRIS/PASSCAL. The detailed investigation of the crust and upper mantle of both projects aims to contribute to a better understanding of the causes for the occurrence of intermediate depth earthquakes in the Vrancea epicentral region and their relationship to the subduction model. In this contribution we will present the project and some first data examples.

Eos, Transactions American Geophysical Union, 2004

The Vrancea region in the South-East Carpathians of Romania is a seismically active area related ... more The Vrancea region in the South-East Carpathians of Romania is a seismically active area related to past or ongoing lithosphere subduction. One of the outstanding questions is whether the subducting slab is attached, detached or in the process of being detached from the overlying lithosphere. GPS campaigns of 3-D crustal displacements in this region, performed by ISES (Netherlands) in collaboration with SFB-461 (Germany) and the University of Bucharest (Romania), are expected to assist in solving this issue. Measurements have been performed in this area since 1995 and the current GPS network consists of more than 50 campaign points and six permanent GPS stations. However, ongoing deformation related to large (Mw > 7) earthquakes that struck the Vrancea region in 1977, 1986 and 1990 could have a considerable contribution to GPS-observed displacement rates. This so-called postseismic deformation results from viscoelastic relaxation of crustal and shallow upper-mantle low-viscosity zones due to the redistributed stress and strain after faulting. Results from the GPS campaigns combined with numerical postseismic deformation modelling indicate that postseismic relaxation is even the dominant mechanism for present-day horizontal crustal displacements in the Vrancea region. This suggests small (< 1 - 2 mm/yr) to insignificant ongoing plate convergence. Vector solution directions are not very sensitive to the earth model, while magnitudes agree for a seismically and tectonically consistent earth model for the Vrancea region. This has important implications for interpreting neotectonic processes in the Carpathians.

Geophysical Journal International, 2011

We relocated the six large-magnitude (5.2 < Mw < 6.2) earthquakes of the destructive, tsunamigeni... more We relocated the six large-magnitude (5.2 < Mw < 6.2) earthquakes of the destructive, tsunamigenic Aysen seismic swarm, which occurred from 2007 January-October in Patagonian Chile. We used P and SH arrival times from near-source stations of a temporary seismic network fortuitously deployed in the area when the swarm began, and also traveltimes to stations of the permanent global networks, to locate the 2007 January 23, Mw 5.2 earthquake, the first of the six large magnitude events. This earthquake's hypocentre lies at shallow depth (<10 km) on the eastern strand of a major intraarc shear zone, the dextral Liquiñe-Ofqui fault zone. Using the hypocentre of the January 23 earthquake as a fixed location, we relocated the five other large magnitude Aysen earthquakes by joint hypocentral determination. Four of these five events also occurred at shallow depth on the eastern strand Liquiñe-Ofqui fault, whereas the 2007 April 2, earthquake occurred some 45 km to the west on the Aysen fault, a strike-slip duplex fault that segments the area between the eastern and western Liquiñe-Ofqui fault strands. The five earthquakes on the Liquiñe-Ofqui fault were all produced by dextral slip on ˜N-S nodal planes approximately parallel to the mapped trace of the fault. The April 2 earthquake resulted from normal slip on the Aysen fault. Modelling of Coulomb stress changes on the nodal planes of the April 2 earthquake shows that the cumulative slip on the Liquiñe-Ofqui fault strand could have triggered the April 2 earthquake. Similarly, the April 2 earthquake may have triggered the Mw 6.2 April 21 earthquake, which caused mass wasting into Aysen Fjord, generating a destructive tsunami. The system of channels and fjords in the study region is a major shipping route around South America, and therefore careful evaluation of the seismic hazard is warranted.

Eos, Transactions American Geophysical Union, 1998

Geophysical experiments next year in Romania may provide insight into a common but short-lived se... more Geophysical experiments next year in Romania may provide insight into a common but short-lived seismic process that can be observed and understood at only one spot on Earth at present. About 150 stations will be set up in the Vrancea area in the southeast Carpathian Mountains to, in effect, record the terminal phase of the detachment of a subducting slab of oceanic lithosphere. This is a major regional tomographic study using a large number of broadband seismometers, which will operate for 6 months. Images will be used for hazard assessment as well as for a delineation of detachment history.Active subduction of oceanic lithosphere at convergent plate boundaries involves earthquakes, magmatism, metamorphism, and deformation—some of the most vivid manifestations of any plate tectonic process. The initiation and termination of subduction, however, remains relatively poorly understood. When convergence of lithospheric plates ceases and the suction force of the subducting plate becomes negligible, the subducting slab moves into an almost vertical position. If subduction occurs in an arcuate geometry, the slab is likely to be segmented.

More than half of the Earth's population lives within the confines of the Tethyan tectonic collis... more More than half of the Earth's population lives within the confines of the Tethyan tectonic collision belt (Figure 1), a high-risk zone that contains at least 20 of the world's “mega-cities.” During the 20th century alone, collision-related seismicity and explosive volcanism (Figure 2) caused over a million deaths and catastrophic economic losses in this region. Destructive volcanism results mostly from the eruption of viscous, volatile-rich magma generated near converging or colliding plate margins, while the most damaging earthquakes are produced by post-collision tectonic thrusting and strike-slip faulting. An exploratory program has been initiated to coordinate research in the Tethyan region, appraise the role of collision-related mantle-dynamics in seismicity and volcanism, and assess their potential significance in mitigating seismic and volcanic hazards across the entire Tethyan belt.

Gsa Today, 2010

... Cande et al., 1987; Bangs et al., 1992; Lagabrielle et al., 2004; Ranero et al., 2006), as we... more ... Cande et al., 1987; Bangs et al., 1992; Lagabrielle et al., 2004; Ranero et al., 2006), as well as important differences between structures, morphology, and evolution in foreland areas north and south, and backarc areas well east of the present triple junction (Ramos, 1989; Flint ...