unmapped Léogâne fault, a secondary transpressional structure located close to the Enriquillo fau... more unmapped Léogâne fault, a secondary transpressional structure located close to the Enriquillo fault, the major fault system assumed to be the primary source of seismic hazard for southern Haiti. In the absence of a precise aftershock catalog, previous estimations of coseismic slip had to infer the rupture geometry from geodetic and/ or seismological data. Here we use a catalog of precisely relocated aftershocks begin-ning one month after the event and covering the following 5 months to constrain the rupture geometry, estimate a slip distribution from an inversion of Global Positional Systems (GPS), Interferometric Synthetic Aperture Radar (InSAR) and coastal uplift data, and calculate the resulting changes of Coulomb failure stress on neighboring faults. The relocated aftershocks confirm a north-dipping structure consistent with the Léogâne fault, as inferred from previous slip inversions, but with two subfaults, each corresponding to a major slip patch. The rupture increased Coulom...
Symithe, Steeve J. PhD, Purdue University, May 2016. Present Day Plate Boundary Deformation in th... more Symithe, Steeve J. PhD, Purdue University, May 2016. Present Day Plate Boundary Deformation in the Caribbean And Crustal Deformation on Southern Haiti . Major Professor: Andrew W. Freed. The Caribbean plate and its boundaries with North and South America, marked by subduction and large intra-arc strike-slip faults, are a natural laboratory for the study of strain partitioning and interseismic plate coupling in relation to large earthquakes. In this work, I use the available campaign and continuous GPS measurements in the Caribbean to derive a regional velocity field expressed in a consistent reference frame. I use this velocity field as input to a kinematic model where surface velocities result from the rotation of rigid blocks bounded by locked faults accumulating interseismic strain, while allowing for partial locking along the Lesser Antilles, Puerto Rico, and Hispaniola subduction. This improved GPS velocity field in the Lesser Antilles excludes more than 3 mm/yr of strain accum...
It has been proposed that interseismic coupling along the Lesser Antilles subduction interface co... more It has been proposed that interseismic coupling along the Lesser Antilles subduction interface could be responsible for subsidence observed over the past 125,000 to 100 years inferred from geological data on Quaternary coral terraces and active micro-atolls in the central part of the arc. However, horizontal GNSS velocities show that the Lesser Antilles subduction zone is currently experiencing low interseismic coupling, meaning that little to no elastic strain currently builds up as the North- and South American plates subduct beneath the Caribbean plate. Here we show, using modern geodetic data, a general subsidence of the Lesser Antilles island arc at 1-2 mm/yr over the past 20 years, in agreement with the ~100-year trend of 1.3 ± 1.1 mm/yr subsidence derived from coral micro-atolls in eastern Martinique. Using elastic dislocation models, we show that a locked, or partially locked subduction interface would produce uplift of the island arc, opposite to present-day and recent geol...
The Caribbean–North America plate boundary in the northeastern Caribbean shows a remarkable examp... more The Caribbean–North America plate boundary in the northeastern Caribbean shows a remarkable example of along-strike transition from plate boundary–normal subduction in the Lesser Antilles, oblique subduction with no strain partitioning in Puerto Rico, and oblique subduction/collision with strain partitioning further west in Hispaniola. We show that this segmentation is well marked in the interseismic strain, as measured using space geodetic data, and in the Neogene deformation regime, as derived from geological observations. Hence, interseismic segmentation, which reproduces the geological segmentation persistent over a long time interval, is inherited from the geological history and long-term properties of the plate boundary. This result is relevant to the assessment of seismic hazard at convergent plate boundaries, where geodetic measurements often show interseismic segmentation between fully–and partially–coupled plate interface regions. 2015 Académie des sciences. Published by E...
Journal of Geophysical Research: Solid Earth, 2021
An important, but originally unexpected, outcome of geodetic measurements at subduction plate bou... more An important, but originally unexpected, outcome of geodetic measurements at subduction plate boundaries over the past 20 years is that some are locked, therefore building-up elastic stresses to be released in large (M w > 7.5) megathrust earthquakes, while others appear to slip aseismically at a rate close or equal to the plate convergence rate, without generating large events. The northern Honshu subduction zone in Japan is an example of the former, with a mechanically locked plate interface and resulting elastic strain measurable on land, as documented in the decades preceding the
A network of “personal seismometers” is intended to complement Haiti’s national seismic network t... more A network of “personal seismometers” is intended to complement Haiti’s national seismic network to engage and inform residents about earthquake hazards and preparation.
Complex networks of high-tech sensors are tough to operate and maintain in developing countries –... more Complex networks of high-tech sensors are tough to operate and maintain in developing countries – but new low-costs, low-maintenance instruments may help. Because they are “connected objects” they also provide new opportunities to engage the civil society in citizen-science. Here we describe a seismological instrumentation experiment in Haiti with sensors that cost less than 500$ and can be installed at individuals, businesses, and schools. We seek to test how such instruments can (1) complement the national seismic network for regional earthquake location and magnitude determination, and (2) open a new communication gateway between seismologists and the civil society.
Earthquake risk reduction approaches classically apply a top-down model where scientific informat... more Earthquake risk reduction approaches classically apply a top-down model where scientific information is processed to deliver risk mitigation measures and policies understandable by all, while shielding end-users from the initial, possibly complex, information. Alternative community-based models exist but are rarely applied at a large scale and rely on valuable, but non-scientific, observations and experiences of local populations. In spite of risk reduction efforts based on both approaches, changes in behaviour or policies to reduce earthquake risk are slow or even non-existent, in particular in developing countries. Here we report on the initial stage of a project that aims at testing, through a participatory seismology experiment in Haiti-a country struck by a devastating earthquake in January 2010-whether public or community involvement through the production and usage of seismic information can improve earthquake awareness and, perhaps, induce grassroots protection initiatives. This experiment is made possible by the recent launch of very low-cost, plug-and-play, Raspberry Shake seismological stations, the relative ease of access to the internet even in developing countries such as Haiti, and the familiarity of all with social networks as a way to disseminate information. Our early findings indicate that 1) the seismic data collected is of sufficient quality for real-time detection and characterization of the regional seismicity, 2) citizens are in demand of earthquake information and trust scientists, even though they appear to see earthquakes through the double lens of tectonics and magic/ religion, 3) the motivation of seismic station hosts has allowed data to flow without interruption for more than a year, including through a major political crisis in the Fall of 2019 and the current COVID19 situation. At this early stage of the project, our observations indicate that citizen-seismology in a development context has potential to engage the public while collecting scientifically-relevant seismological information.
The ∼3 M inhabitant capital region of Haiti, severely affected by the devastating January 12, 201... more The ∼3 M inhabitant capital region of Haiti, severely affected by the devastating January 12, 2010, M7.0 earthquake, continues to expand at a fast rate. Accurate characterization of regional earthquake sources is key to inform urban development and construction practices through improved regional seismic hazard estimates. Here we use a recently updated Global Positioning System (GPS) data set to show that seismogenic strain accumulation in southern Haiti involves an overlooked component of shortening on a south-dipping reverse fault along the southern edge of the Cul-de-Sac basin, in addition to the well-known component of leftlateral strike-slip motion. This tectonic model implies that ground shaking may be twice that expected if the major fault was purely strike-slip, as assumed in the current seismic hazard map for the region.
unmapped Léogâne fault, a secondary transpressional structure located close to the Enriquillo fau... more unmapped Léogâne fault, a secondary transpressional structure located close to the Enriquillo fault, the major fault system assumed to be the primary source of seismic hazard for southern Haiti. In the absence of a precise aftershock catalog, previous estimations of coseismic slip had to infer the rupture geometry from geodetic and/ or seismological data. Here we use a catalog of precisely relocated aftershocks begin-ning one month after the event and covering the following 5 months to constrain the rupture geometry, estimate a slip distribution from an inversion of Global Positional Systems (GPS), Interferometric Synthetic Aperture Radar (InSAR) and coastal uplift data, and calculate the resulting changes of Coulomb failure stress on neighboring faults. The relocated aftershocks confirm a north-dipping structure consistent with the Léogâne fault, as inferred from previous slip inversions, but with two subfaults, each corresponding to a major slip patch. The rupture increased Coulom...
Symithe, Steeve J. PhD, Purdue University, May 2016. Present Day Plate Boundary Deformation in th... more Symithe, Steeve J. PhD, Purdue University, May 2016. Present Day Plate Boundary Deformation in the Caribbean And Crustal Deformation on Southern Haiti . Major Professor: Andrew W. Freed. The Caribbean plate and its boundaries with North and South America, marked by subduction and large intra-arc strike-slip faults, are a natural laboratory for the study of strain partitioning and interseismic plate coupling in relation to large earthquakes. In this work, I use the available campaign and continuous GPS measurements in the Caribbean to derive a regional velocity field expressed in a consistent reference frame. I use this velocity field as input to a kinematic model where surface velocities result from the rotation of rigid blocks bounded by locked faults accumulating interseismic strain, while allowing for partial locking along the Lesser Antilles, Puerto Rico, and Hispaniola subduction. This improved GPS velocity field in the Lesser Antilles excludes more than 3 mm/yr of strain accum...
It has been proposed that interseismic coupling along the Lesser Antilles subduction interface co... more It has been proposed that interseismic coupling along the Lesser Antilles subduction interface could be responsible for subsidence observed over the past 125,000 to 100 years inferred from geological data on Quaternary coral terraces and active micro-atolls in the central part of the arc. However, horizontal GNSS velocities show that the Lesser Antilles subduction zone is currently experiencing low interseismic coupling, meaning that little to no elastic strain currently builds up as the North- and South American plates subduct beneath the Caribbean plate. Here we show, using modern geodetic data, a general subsidence of the Lesser Antilles island arc at 1-2 mm/yr over the past 20 years, in agreement with the ~100-year trend of 1.3 ± 1.1 mm/yr subsidence derived from coral micro-atolls in eastern Martinique. Using elastic dislocation models, we show that a locked, or partially locked subduction interface would produce uplift of the island arc, opposite to present-day and recent geol...
The Caribbean–North America plate boundary in the northeastern Caribbean shows a remarkable examp... more The Caribbean–North America plate boundary in the northeastern Caribbean shows a remarkable example of along-strike transition from plate boundary–normal subduction in the Lesser Antilles, oblique subduction with no strain partitioning in Puerto Rico, and oblique subduction/collision with strain partitioning further west in Hispaniola. We show that this segmentation is well marked in the interseismic strain, as measured using space geodetic data, and in the Neogene deformation regime, as derived from geological observations. Hence, interseismic segmentation, which reproduces the geological segmentation persistent over a long time interval, is inherited from the geological history and long-term properties of the plate boundary. This result is relevant to the assessment of seismic hazard at convergent plate boundaries, where geodetic measurements often show interseismic segmentation between fully–and partially–coupled plate interface regions. 2015 Académie des sciences. Published by E...
Journal of Geophysical Research: Solid Earth, 2021
An important, but originally unexpected, outcome of geodetic measurements at subduction plate bou... more An important, but originally unexpected, outcome of geodetic measurements at subduction plate boundaries over the past 20 years is that some are locked, therefore building-up elastic stresses to be released in large (M w > 7.5) megathrust earthquakes, while others appear to slip aseismically at a rate close or equal to the plate convergence rate, without generating large events. The northern Honshu subduction zone in Japan is an example of the former, with a mechanically locked plate interface and resulting elastic strain measurable on land, as documented in the decades preceding the
A network of “personal seismometers” is intended to complement Haiti’s national seismic network t... more A network of “personal seismometers” is intended to complement Haiti’s national seismic network to engage and inform residents about earthquake hazards and preparation.
Complex networks of high-tech sensors are tough to operate and maintain in developing countries –... more Complex networks of high-tech sensors are tough to operate and maintain in developing countries – but new low-costs, low-maintenance instruments may help. Because they are “connected objects” they also provide new opportunities to engage the civil society in citizen-science. Here we describe a seismological instrumentation experiment in Haiti with sensors that cost less than 500$ and can be installed at individuals, businesses, and schools. We seek to test how such instruments can (1) complement the national seismic network for regional earthquake location and magnitude determination, and (2) open a new communication gateway between seismologists and the civil society.
Earthquake risk reduction approaches classically apply a top-down model where scientific informat... more Earthquake risk reduction approaches classically apply a top-down model where scientific information is processed to deliver risk mitigation measures and policies understandable by all, while shielding end-users from the initial, possibly complex, information. Alternative community-based models exist but are rarely applied at a large scale and rely on valuable, but non-scientific, observations and experiences of local populations. In spite of risk reduction efforts based on both approaches, changes in behaviour or policies to reduce earthquake risk are slow or even non-existent, in particular in developing countries. Here we report on the initial stage of a project that aims at testing, through a participatory seismology experiment in Haiti-a country struck by a devastating earthquake in January 2010-whether public or community involvement through the production and usage of seismic information can improve earthquake awareness and, perhaps, induce grassroots protection initiatives. This experiment is made possible by the recent launch of very low-cost, plug-and-play, Raspberry Shake seismological stations, the relative ease of access to the internet even in developing countries such as Haiti, and the familiarity of all with social networks as a way to disseminate information. Our early findings indicate that 1) the seismic data collected is of sufficient quality for real-time detection and characterization of the regional seismicity, 2) citizens are in demand of earthquake information and trust scientists, even though they appear to see earthquakes through the double lens of tectonics and magic/ religion, 3) the motivation of seismic station hosts has allowed data to flow without interruption for more than a year, including through a major political crisis in the Fall of 2019 and the current COVID19 situation. At this early stage of the project, our observations indicate that citizen-seismology in a development context has potential to engage the public while collecting scientifically-relevant seismological information.
The ∼3 M inhabitant capital region of Haiti, severely affected by the devastating January 12, 201... more The ∼3 M inhabitant capital region of Haiti, severely affected by the devastating January 12, 2010, M7.0 earthquake, continues to expand at a fast rate. Accurate characterization of regional earthquake sources is key to inform urban development and construction practices through improved regional seismic hazard estimates. Here we use a recently updated Global Positioning System (GPS) data set to show that seismogenic strain accumulation in southern Haiti involves an overlooked component of shortening on a south-dipping reverse fault along the southern edge of the Cul-de-Sac basin, in addition to the well-known component of leftlateral strike-slip motion. This tectonic model implies that ground shaking may be twice that expected if the major fault was purely strike-slip, as assumed in the current seismic hazard map for the region.
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Papers by Steeve Symithe