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The geodynamic complexity in the western Mexican margin is controlled by the multiple interactions between the Rivera, Pacific, Cocos, and North American plates, as evidenced by a high seismicity rate, most of whose hypocenters are poorly located. To mitigate this uncertainty with the aim of improving these hypocentral locations, we undertook the TsuJal Project, a passive seafloor seismic project conducted from April to November 2016. In addition to the Jalisco Seismic Network, 10 LCHEAPO 2000 Ocean Bottom Seismometers (OBSs) were deployed by the BO El Puma in a seafloor array from the Islas Marías Archipelago (Nayarit) to the offshore contact between the states of Colima and Michoacan. We located 445 earthquakes in four or more OBSs within the deployed array. Most of these earthquakes occurred in the contact region of the Rivera, Pacific, and Cocos plates, and a first analysis suggests the existence of three seismogenic zones (West, Center, and East) along the Rivera Transform fault that can be correlated with its morphological expression throughout the three seismogenic zones. The seismicity estimates that the Moho discontinuity is located at 10 km depth and supports earlier works regarding the West zone earthquake distribution. Subcrustal seismicity in the Central zone suggests that the Intra-Transform Spreading Basin domain is an ultra-low spreading ridge. A seismic swarm occurred during May and June 2016 between the eastern tip of the Paleo-Rivera Transform fault and the northern tip of the East Pacific Rise-Pacific Cocos Segment, illuminating some unidentified tectonic feature.

The crustal structure around the Islas Marías Archipelago has been debated for a long time. An important unresolved question is where the Rivera-North American plate subduction ends and the Tamayo fracture zone begins, from SE to NW. Results from the TsuJal project have shed light on the northwesternmost part of the Jalisco block structure. It is now clear that Sierra de Cleofas and the Islas Marías Escarpment comprise the northwestern continuation of the Middle America trench. However, other questions remain. In this paper, we present the structure of the shallow and deep crust and the upper mantle of the Islas Marías western region through the integration of multichannel seismic reflection, wide-angle seismic bathymetric and seismicity data, including records of an amphibious seismic network, OBS, and portable seismic stations, purposely deployed for this project, providing an onshore-offshore transect of 310 km length. Our findings disclose new evidence of the complex structure of the Rivera plate that dips 8°–9° underneath the NW Jalisco block as revealed by two seismic profiles parallel to the Islas Marías Escarpment. Moreover, we find five sedimentary basins and active normal faults at the edges of tectonic structures of the E-W oriented West Ranges and the N-S trending Sierra de Cleofas. Furthermore, the Sierra de Cleofas is the beginning of the active subduction of the Rivera plate beneath North America. The oceanic crust thickens and submerges towards the south while is coupled with the continental crust, from 6 km at the northern ends of the seismic profiles to 15 km in the contact region and 24 km at the coast and southern ends of them. The continental Moho was not fully characterized because of the geometry of the seismic transects, but a low-velocity layer associated with Rivera Plate subduction was observed beneath the Jalisco Block. Our results constrain the complexity of the area and reveal new structural features from the oceanic to continental crust and will be pivotal to assess geohazards in this area.

The tectonic interaction between the Rivera and North American plates north of the Bahía de Banderas is poorly understood. The nature of the crust and where the subduction ends in the western part of the Islas Marias Archipelago are still controversial. Based on new geophysical data provided by the TsuJal project, we present the shallow and deep crustal structure of the Rivera–North American plate contact zone along two seismic transects, TS09b and RTSIM01b, and the bathymetry obtained across the northern region of María Madre Island. Detailed bathymetric analysis allowed mapping of a series of lineaments along the study region, with two main preferred tendencies (020–050° and 290–320°) associated with the evolution of the Pacific-Rivera rise and the transform faults of the Gulf of California, respectively. The shallow structure is characterized by five sedimentary basins without deformation, whose horizons are subparallel, suggesting that the sediment deposition occurred after the extension process ended. The deep structure corresponds to a transition between oceanic crust (Rivera Plate), with an average thickness of ∼10 km to the Islas Marías Escarpment, and a thinned continental crust, whose thickness increases toward the continent until it reaches 28 km, with a dip angle of 7–10°. The absence of an accretionary prism suggests that the subduction process of the Rivera Plate beneath the North American Plate to the north of Islas Marías has ceased. In this study, we determined that the morphological expression of the northern limit of the Rivera Plate corresponds to the Islas Marías Escarpment.

Ocean hydrothermal activity is well known from deep-sea studies; however, few studies have been reported at shallow depth. A shallow submarine hydrothermal system at Punta Mita described in 2000 was studied to determine the grain size classification of the marine sediments of this hydrothermal system. Three sites with hydrothermal activity were included. Each one was divided into three areas: with hydrothermal activity, intermediate, and out of hydrothermal activity. In each area, two sediment cores were randomly collected by scuba diving (number of sediment cores = 18). All sediment samples were subjected to a previous treatment, to eliminate salts and organic matter. The grain sizes were sieved and then classified following the Udden–Wentworth scale. A principal coordinate analysis was performed to determine if there was any association of the statistical moments with the areas and sites of study. The textural composition of the sediments in the hydrothermal influence areas is sand, where the very fine sand is the dominant grain size, which was confirmed with the mean moment. The sediments are characteristic of the tidal areas, except for those sediments in the areas with hydrothermal activity.

En este trabajo se modela la fuente sísmica del tsunami de Jalisco-Colima del 9 de octubre de 1995 ajustando los resultados del modelo numérico del tsunami para reproducir adecuadamente las alturas de inundación del tsunami documentadas in situ durante los trabajos de reconocimiento del área afectada por el tsunami. La fuente sísmica corresponde a un sismo de magnitud Mw∼8.0 con un área de ruptura A = 9000 km2, L = 150 km, W = 60 km, con dislocación cosísmica heterogénea: dislocación de 1 m en los primeros 60 km a lo largo del plano de falla iniciando en el extremo NW, mar adentro frente a Chalacatepec y Chamela, y dislocación de 3 m en los restantes 90 km, mar adentro frente a Tenacatita, Navidad y Manzanillo. Como se esperaba, la fuente sísmica obtenida en este estudio es un modelo simplificado en comparación con la obtenida invirtiendo datos sísmicos y de GPS. Sin embargo, el hecho de que este modelo simplificado reproduzca aproximadamente la dislocación cosísmica y el área de ruptura y su localización, es importante para validar la fuente sísmica de aquellos tsunamis históricos de los que únicamente se cuenta con algunos testimonios y relatos vagos de sus efectos y de los cuales no existen registros sísmicos ni del nivel del mar. doi: https://doi.org/10.1016/j.gi.2015.04.010

A study was carried out to determine the causes of the sudden disappearance of Mismaloya Beach, Jalisco (Mexico), in the early hours of 8 September 2001. This event occurred in a few hours, leaving behind a 2-m-high beach scarp as well as restaurants and palapas flooded by the ocean. Bathymetric and beach profiles were done to know the morphology and evolution of the coastal zone, and the bathymetry and eroded sediment volumes were obtained. Analyses were made of the coastal profile slopes, the physical characteristics of the sediments and the zone hydrodynamics. The event was caused by a slump of the sediments that lay over very steep slopes of the coastal profile (up to 18º), as a consequence of the weight and tixotrophic properties of the sediments.