Present day plate boundary deformation in the Caribbean and crustal deformation on southern Haiti

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 earth- quakes. 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 inter- seismic 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 accumulation on the Lesser Antilles-Puerto Rico subduction plate interface, which appears essentially uncoupled. The transition from a coupled to an uncoupled subduction in the northeastern Caribbean coincides with a transition in the long-term geological behavior of the Caribbean plate margin from compressional (Hispaniola) to extensional (Puerto Rico and Lesser Antilles). Also in Haiti, the ∼3 M inhabitant capital region that was severely affected by the devastating M7.0, 2010 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. I also use this improved GPS data set and 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 left-lateral 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 regio

30 years in the life of an active submarine volcano: A time-lapse bathymetry study of the Kick-‘em-Jenny Volcano, Lesser Antilles

Effective monitoring is an essential part of identifying and mitigating volcanic hazards. In the submarine environment this is more difficult than onshore because observations are typically limited to land-based seismic networks and infrequent shipboard surveys. Since the first recorded eruption in 1939, the Kick-‘em-Jenny (KeJ) volcano, located 8km off northern Grenada, has been the source of 13 episodes of T-phase signals. These distinctive seismic signals, often coincident with heightened body-wave seismicity, are interpreted as extrusive eruptions. They have occurred with a recurrence interval of around a decade, yet direct confirmation of volcanism has been rare. By conducting new bathymetric surveys in 2016 and 2017 and reprocessing 4 legacy datasets spanning 30 years we present a clearer picture of the development of KeJ through time. Processed grids with a cell size of 5m and vertical precision on the order of 1-4m allow us to correlate T-phase episodes with morphological changes at the volcano's edifice. In the time-period of observation 7.09x106 m3 of material has been added through constructive volcanism – yet 5 times this amount has been lost through landslides. Limited recent magma production suggests that KeJ may be susceptible to larger eruptions with longer repeat times than have occurred during the study interval, behavior more similar to sub-aerial volcanism in the arc than previously thought. T-phase signals at KeJ have a varied origin and are unlikely to be solely the result of extrusive submarine eruptions. Our results confirm the value of repeat swath bathymetry surveys in assessing submarine volcanic hazards

Citizen seismology helps decipher the 2021 Haiti earthquake

5 pages, 4 figures, supplementary materials https://doi.org/10.1126/science.abn1045.-- Data and materials availability: All data and code used in this study are openly available. RADAR data can be obtained through ESA (Sentinel) or JAXA (Alos-2). Aftershock data can be obtained from https://ayiti.unice.fr/ayiti-seismes/ (7). The codes used to process or model the data are published and public (8). The catalog of high-precision earthquake relocated with the NLL-SSST-coherence procedure (SM4) is available as supplementary dataOn 14 August 2021, the moment magnitude (Mw) 7.2 Nippes earthquake in Haiti occurred within the same fault zone as its devastating 2010 Mw 7.0 predecessor, but struck the country when field access was limited by insecurity and conventional seismometers from the national network were inoperative. A network of citizen seismometers installed in 2019 provided near-field data critical to rapidly understand the mechanism of the mainshock and monitor its aftershock sequence. Their real-time data defined two aftershock clusters that coincide with two areas of coseismic slip derived from inversions of conventional seismological and geodetic data. Machine learning applied to data from the citizen seismometer closest to the mainshock allows us to forecast aftershocks as accurately as with the network-derived catalog. This shows the utility of citizen science contributing to our understanding of a major earthquakeThis work was supported by the Centre National de la Recherche Scientifique (CNRS) and the Institut de Recherche pour le Développement (IRD) through their “Natural Hazard” program (E.C., S.S., T.M., B.D., F.C., J.P.A., J.C., A.D., D.B., S.P.); the FEDER European Community program within the Interreg Caraïbes “PREST” project (E.C., S.S., D.B.); Institut Universitaire de France (E.C., R.J.); Université Côte d’Azur and the French Embassy in Haiti (S.P.); the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant no. 758210, Geo4D project to R.J. and grant no. 805256 to Z.D.); the French National Research Agency (project ANR-21-CE03-0010 “OSMOSE” to E.C. and ANR-15-IDEX-01 “UCAJEDI Investments in the Future” to Q.B.); the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant no. 949221 to Q.B.); and HPC resources of IDRIS (under allocations 2020-AD011012142, 2021-AP011012536, and 2021-A0101012314 to Q.B.With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S)Peer reviewe

Dehydration of subducting slow-spread oceanic lithosphere in the Lesser Antilles

Subducting slabs carry water into the mantle and are a major gateway in the global geochemical water cycle. Fluid transport and release can be constrained with seismological data. Here we use joint active-source/local-earthquake seismic tomography to derive unprecedented constraints on multi-stage fluid release from subducting slow-spread oceanic lithosphere. We image the low P-wave velocity crustal layer on the slab top and show that it disappears beneath 60–100 km depth, marking the depth of dehydration metamorphism and eclogitization. Clustering of seismicity at 120–160 km depth suggests that the slab’s mantle dehydrates beneath the volcanic arc, and may be the main source of fluids triggering arc magma generation. Lateral variations in seismic properties on the slab surface suggest that serpentinized peridotite exhumed in tectonized slow-spread crust near fracture zones may increase water transport to sub-arc depths. This results in heterogeneous water release and directly impacts earthquakes generation and mantle wedge dynamics

The 28 January 2020, Mw7.7, Cayman Trough / Oriente Fault, Supershear Earthquake Rupture

The largest magnitude strike-slip event of the instrumental seismology era along the northern Caribbean plate boundary, with a moment magnitude of 7.7, occurred on 28 January 2020 on the Oriente transform fault, along the northern edge of the Cayman Trough, west of Cuba. We use local, regional, and global seismic waveforms and coseismic geodetic offsets, to produce high-resolution rupture models for both the low-frequency (~ 0.02 Hz) and high-frequency (~ 1 Hz) components of the rupture using a finite fault kinematic inversion and back-projection imaging, respectively. We document a rupture that propagated predominantly unilaterally westward, with an initial phase at subshear speed for 20–-30~s and over 40 to 50~km, followed by an acceleration to supershear speed that persisted all the way to the western end of the rupture, for 40~s and over about 200~km. Supershear rupture speed is consistent with strong motion observations of low ground acceleration levels in the near-field of the fault and low aftershock production in numbers and moment release. The rupture followed a very linear, unsegmented portion of the Oriente fault that had not experienced significant seismic activity for at least a century. Observational evidence and models indicate that the 28 January 2020, Mw7.7 earthquake, supershear over most of its length, had a smooth rupture process along a simple linear fault segment where earthquake nucleation is infrequent and interseismic locking depth shallow, two characteristics that may explain this unusually large magnitude supershear event

Foundation News

The 2010 7.0 MW earthquake that struck southern Haiti had a devastating impact on the country. It is estimated that 230,000 people were killed, 300,000 injured, and 2 million displaced ( https://www.gao.gov/assets/660/658445.pdf ). Since that time, the city of Port-au-Prince, with approximately 3 million inhabitants, continues to expand at a fast pace. Accurate characterization of the regional earthquake hazard, particularly along the active Enriquillo Fault, is key to informing urban development and construction practices during the long reconstruction phase through which Haiti continues to progress. Our team recently showed that the seismic hazard map currently in use is significantly incomplete for the Port-au-Prince metropolitan area. This conclusion was reached based on the discovery of an overlooked component of north-south shortening along the Cul-de-Sac Plain to the north of the Massif de la Selle using space geodetic measurements from GPS. Therefore, new regional seismic hazard estimates are needed to better inform development in order to help lessen the devastating impact of future seismic activity. </jats:p

Coseismic slip distribution of the 2010 m7.0 Haiti earthquake and resulting stress changes on regional faults

The Mw 7.0 January 12, 2010, Haiti earthquake ruptured the previously unmapped Léogâne Fault, a secondary transpressional fault located close to the Enriquillo Plantain Garden Fault (EPGF), 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 covering the 6 months following the event to constrain the rupture geometry, estimate a slip distribution from an inversion of GPS, 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. Our updated source model involves two subfaults, each corresponding to a major slip patch. The eastern one combines strike-slip and dip-slip, while the western one is mostly strike-slip. Overall, the event released 68 % of left-lateral strike-slip and 32 % of dip-slip reverse seismic moment, consistent with secular strain accumulation in southern Haiti from regional GPS studies. Coulomb failure stress changes caused by the coseismic rupture show that the cluster of reverse faulting earthquakes, one as large as M 5.9, that were observed to the west of the coseismic rupture coincident with the offshore Trois Baies fault were likely triggered by the main shock. We find increased stresses on the Enriquillo fault to the west of the January 12, 2010 rupture (Miragoâne area, ∼3 bars) and to the east near Port-au-Prince (0.3 to ∼1 bar). Other regional faults do not show significant increase of static stresses at seismogenic depth. Increased coseismic stress changes on the Trois Baies fault and portions of the Enriquillo fault to the west and east of the Léogâne rupture are a concern as this could advance the timing of future events on those faults, which are all capable of magnitude 7 or greater events

Present day plate boundary deformation in the Caribbean and crustal deformation on southern Haiti

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 earth- quakes. 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 inter- seismic 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 accumulation on the Lesser Antilles-Puerto Rico subduction plate interface, which appears essentially uncoupled. The transition from a coupled to an uncoupled subduction in the northeastern Caribbean coincides with a transition in the long-term geological behavior of the Caribbean plate margin from compressional (Hispaniola) to extensional (Puerto Rico and Lesser Antilles). Also in Haiti, the ∼3 M inhabitant capital region that was severely affected by the devastating M7.0, 2010 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. I also use this improved GPS data set and 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 left-lateral 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

Geodetic evidence for a significant component of shortening along the northern Caribbean strike-slip plate boundary in southern Haiti

&amp;lt;p&amp;gt;GPS measurements within the transform Caribbean&amp;amp;#8211;North American plate boundary in Hispaniola, Greater Antilles, with five additional years of data at continuous sites and additional campaign measurements, significantly improve the resulting velocities of earlier works. In a Caribbean-fixed frame, velocities at sites located along the island's southern coast are small (&amp;lt; 2 mm/yr), indicating that the offshore active faults mapped south of Haiti are currently slipping at very low rates. In the Southern Peninsula, velocities are oriented westward, parallel to the Enriquillo fault zone, consistent with strain accumulation on that left-lateral strike-slip fault. North of the Southern Peninsula, including the Gon&amp;amp;#226;ve island, velocities are consistently trending SW to WSW, oblique to the east-west direction of the plate boundary. This difference in velocity trend between the Southern Peninsula and areas to the north indicates regional shortening north of the southern Peninsula with an amplitude of 6-7 mm/yr of plate boundary-normal shortening. Geologic and high-resolution seismic data show that this shortening is likely taking place just at the northern coast of the Southern Peninsula, localized on a north-verging reverse fault system offshore the north coast of the Southern Peninsula of Haiti. This reverse fault system extends westward a similar fault system previously described on the southern edge of the Cul-de-Sac Plain, together delineating what we call the &amp;quot;J&amp;amp;#233;r&amp;amp;#233;mie-Malpasse&amp;quot; reverse-fault system. This fault zone marks the boundary between the Caribbean Large Igneous Province to the south (CLIP), an oceanic plateau outcropping in the Southern Peninsula, and terranes of island arc crust to the north, a rare case of ongoing obduction in a transform context. This setting, consistent with the source mechanisms of the Mw7.0 January 2010 and Mw7.2 August 20121 earthquakes in southern Haiti,&amp;amp;#160;has significant implications in terms of regional seismic hazard.&amp;lt;/p&amp;gt;</jats:p