The Oaxaca region represents the most seismically active zone in Mexico, driven by the subduction of the Cocos Plate beneath the North American Plate. The historical record indicates a high recurrence rate: 77 earthquakes of magnitude M > 7.0 have occurred over the last 517 years, averaging one event every 6.7 years. This study reevaluates 20 major events (M > 7.0) that occurred between 1928 and 1982, a period historically characterized by hypocentral location discrepancies exceeding 100 km. To resolve these uncertainties, we quantified the robust spatial constraints of the 1928–1937 sequence by analyzing S-P intervals derived from historical Wiechert seismograms at the Tacubaya and Veracruz stations, propagating reading errors into well-bounded circular-trapezoid rupture regions. Furthermore, seismicity occurring between 1950 and 1982 was relocated utilizing the Joint Hypocenter Determination method. For the 1928-1982 interval, coastal earthquakes are grouped into two distinct sequences (Series 1 and Series 2), which are subsequently evaluated against a modern sequence (Series 3, 1995-2020). Spatial analysis reveals that while no major event ruptured the same epicentral zone within the 1928–1982 window, the rupture patches of the modern Series 3 significantly overlap with those of the preceding two series, defining clear intra-domain recurrence intervals. Analysis of re-evaluated focal mechanisms indicates that while coastal events generally align with the plate subduction direction, the anomalous August and October 1928 events provide evidence of a structural discontinuity beneath the Río Verde area. Based on these relocations, uncertainties, and focal mechanisms, we propose a segmented subduction interface divided into main blocks (Western and Eastern sections) separated by a Central transition zone. This configuration successfully clarifies the transition from the Mexican to the Central American subduction zones and provides a more robust framework for seismic-hazard assessment along the Oaxaca margin.

A digital bathymetric model was generated for a specific area of the Punta Mita Shallow-Water Hydrothermal System, and the spatial distribution of some active hydrothermal vents was mapped. Bathymetric data acquired with a single-beam echosounder were interpolated at 2 m resolution, and vent locations were analyzed using spatial and kernel density methods. The results provide a first-order, continuous geomorphological approach of the seabed in this area, agreeing in certain aspects with the previously reported fault system, but also showing new lineaments, depressions, and morphological features associated with hydrothermal activity.

In this study, we evaluated the performance of SAIPy, an open-source Python package for deep learning-based seismic data analysis, by applying its single-station monitoring tools and extending its use to a seismic network based approach, using data from a local seismic network deployed in a Caldera. Although the integrated models into SAIPy for earthquake detection,magnitude estimation, seismic phase picking, and P-wave polarity classification, were originally trained on tectonic signals, we assess their performance in a more complex seismic environment that includes volcano-tectonic events, along with signal interference from distant earthquakes.We also demonstrate the advantages of integrating outputs using multiple stations to improve event detection. SAIPy was able to identify a significantly larger number of local events than those included in previously published catalogs. SAIPy demonstrated reliable phase picking and P-wave polarity estimation, particularly for local volcano-tectonic events, with some limitations observed in the magnitude estimation for complex volcanic signals. These results support the utility of SAIPy for processing continuous seismic data and suggest that future retraining using data with physically standardized units, removing instrumental response, and including data from more diverse seismic sources, could improve its generalization for magnitude estimation to complex scenarios and different seismic networks and sensor types.

The Islas Marias Archipelago is located south of the Gulf of California. This study presents a structural geologic analysis of Maria Madre Island, coupled with a detailed bathymetric survey of the surrounding area. Our goal is to delineate the deformation geometry and identify new morphostructural features in the region. Bedding tilting coincided with normal faulting of the lower member of the Ojo de Buey sequence, likely at the end of the Pliocene or the beginning of the Pleistocene, associated with the early stage of the Gulf of California rifting. Seismic reflection profiles from previous studies indicate that the West Ranges are within a thinned continental crust, structurally controlled by the Maria, Magdalena, and South Magdalena faults. Furthermore, a detailed bathymetric survey and orthoimages from the islands revealed structural lineaments in both oceanic and continental crust. In the continental crust, these lineaments have a preferred orientation between 050 degrees to 090 degrees, similar to the faulting trend on Maria Madre Island. However, they are oblique to those in the oceanic crust and mainland Mexico. We propose that Maria Madre Island may have undergone a 50 degrees clockwise rotation. If we apply a counterclockwise rotation of this magnitude to the faults and lineaments in the continental crust of the archipelago and the region west of it, their preferred orientation becomes parallel to the Tamayo Fracture Zone in the oceanic crust, the San Blas fault within the continental shield and, the Tepic-Zacolaco rift extending eastward into mainland Mexico. This suggests that rotation affected the continental crust, either west of Puerto Vallarta, in the archipelago, or the West Ranges, while the oceanic crust remained relatively unaffected. We propose the term "Islas Marias Block" to designate a fragment of continental crust encompassing the archipelago and the West Ranges, which share a common deformation style.

Oaxaca is the most seismically active region in Mexico and one of the most studied using different methodologies. This seismic activity is due to the subduction of the Cocos Plate beneath the North American Plate, which is considered an anomalous subduction zone since it is a truncated continental margin. Seventy-four earthquakes (M> 7.0) have been identified in the last 510 years, which is an average of one earthquake every 6.8 years. The seismic sequence occurred between 1928 and 1937 is the key to understand the regional seismotectonics. The locations of these nine events (M>7.0) reported by different authors differ by more than 100 km for the same earthquake. We relocated the aftershocks of these earthquakes using the seismograms from TAC (Tacubaya) and VCM (Veracruz) stations available at the Seismological Seismic Network (Mexico) archive reading pre-phases S-P. To calibrate these readings, we relocate the seismicity in the region between 1950 and 1982 with the JHD Method using 1978, 1982, 1965 and 1968 earthquakes as Master Events. We look from this catalog the earthquakes registered in TAC and VCM in the period 1950 - 1982 and whose seismograms were in the archive were selected. The S-P prephases in TAC and VCM were read with the same criteria used previously. With these data we fitting a time-distance curve for each station. These curves were used to obtain more reliable aftershock area for each of the coastal earthquakes occurred during the 1928 – 1937 sequence.

The geometry of the Rivera and Cocos plates subduction below the North American plate has been studied using a total of 5337 hypocenters located in the region of Nayarit, Jalisco, Colima, and Michoac & aacute;n states in western Mexico. Our results show that seismic block are well differentiated. Our study supports the hypothesis that the Jalisco subduction zone is composed of two fore-arc blocks, Banderas and Jalisco fore-arc blocks, separated by the Ipala canyon (Bandy fault). In this region, the crustal thickness of the JB is similar to 30 km, whereas the Michoac & aacute;n block is 35 km thick. We identified four crustal blocks along the coast in the JB from shallow seismicity data. Moreover, we found that the Rivera plate is segmented into three sections with different sizes and geometries evidenced by deep seismicity data. There is no evidence of a slab below the CRZ due to seismicity being scarce, except on the coast and the Colima volcano area where deep earthquakes (>70 km) are observed, which could be related to magmatic processes. The seismicity of the subduction process of the Cocos plate appears homogeneous, except for a seismic cluster at the mouth of Coalcom & aacute;n River, where the epicentral area of the 1973 and 2021 earthquakes is located. Our results show that the Cocos plate is subducting with an inclination of 24 degrees-30 degrees and is slightly bent in a northwesterly direction. Therefore, our study suggests that current seismotectonic models of the region should be revised.

Numerous microearthquakes, M L ≤ 3.8, corresponding to background seismicity and swarms were observed from September 3, 2017, to January 1, 2018, mainly in the Tesistán Valley, north of the Guadalajara Metropolitan Zone (GMZ). We located 188 tectonic microearthquakes and identified 11 clusters of similar events from a spatio-temporal analysis and waveform cross-correlations. Our results confirm the presence of continuous seismicity in the GMZ that long went unobserved. Most M L ≥ 2.5 events and some clustered events are located in the northeastern Tesistán, close to the NNE-SSW fault corresponding to the eastern edge of the Zapopan Graben, a structure evidenced by 2015–2016 seismicity. Seismicity recorded during 2020 by a recent local seismic network installed in Zapopan reaffirms that frequent microseismicity is related to active faults that cross the cities of Zapopan and Guadalajara. The microseismicity distribution suggests minor faults with the same orientation and sense of displacement as the main structures bounding the Zapopan Graben, which corresponds to structures known as synthetic faults. This arrangement is common within the Basin and Range tectonic province. The seismicity in the northeast boundary of Jalisco Block is closely related to faults formed by Cenozoic deformation events that might be reactivated due to modern crustal dynamics. Active faults and the possibility of synthetic structures are a hypothesis that necessitates long-term seismic monitoring in order to assess the seismic hazard in the GMZ, which is a crucial factor for urban planning.

We present a new method for location of the source of volcanic harmonic tremor, that employs the Fourier phases of an observed tremor segment recorded at various seismic stations, a condition on the inferred phase at the source, and a search location scheme. We discuss the assumptions and limitations inherent to the proposed method. As an illustration of application to real data, the method is used to locate twenty sources of harmonic tremor occurred at Popocatépetl volcano (Mexico) during the July 2006 tremor episode; the located sources agree quite well with results from other studies of seismicity in this volcano.

El Chichon is the northernmost and youngest volcano of the modern Chiapanecan volcanic arc and is responsible for the deadliest volcanic disaster in Mexico's modern history. Forty years after the eruption, there are still uncertainties in the subsurface architecture of the volcano and its basement. Based on this, we performed aeromagnetic data analyses using reduction-transformation techniques, spectral analysis, and forward modeling to delineate the magnetic rock-strata and to image the boundaries of the magmatic reservoir or regions of molten rock. Results show that the magnetic alignments identified correlate well with the local geological features. Our preferred interpretation of the estimated Curie point depth is as a region of mush composed of crystals and molten rock below the volcano (4.77 km), depicting the transitional sector to a deeper magma reservoir. We compute values of 101.57 degrees C km(-1) and 253 mW center dot m(-2) for the geothermal gradient and conductive heat flux, respectively. In addition, we identify two complementary aquifer formations representing the shallow-local and deeper-regional aquifer units using geomorphology, topographic, and stratigraphic characteristics. The mag-netic anomalies analyzed and the identification of aquifer units in this study provide new detailed information about the geological, geophysical, and hydrogeological conceptual models of the El Chich ' on geothermal system.

Magma and related hydrothermal fluid movement, and their interaction with solid rock, in active volcanic regions, generate a wide variety of seismic waves whose characterization can mitigate the risk of a potential eruption. Located in the western region of the Trans-Mexican Volcanic Belt, Ceboruco Volcano, whose last eruptive period was 1870-1875, is considered to be one of the most hazardous volcanoes in Mexico. We have conducted a detailed study of the seismicity in the surroundings of Ceboruco's volcanic edifice to assess the current state of this volcano. A dense temporary seismic network with 25 seismic stations in an area of 16 km x 16 km was deployed between November 2016 and July 2017, as part of the P-24 project of the CeMIEGeo consortium; this effort has allowed the detection of 81 earthquakes concentrated beneath the crater with depths between 4 and 8 km. In this study, We observe that the recorded seismicity occurs in swarms, and we specifically identify four sequences that we characterize in detail via the first focal mechanisms available for this volcano. Our results suggest a change in the local seismicity distribution compared to earlier observations, which reported seismic activity near the volcano edifice associated with fluid migration along zones of weakness related to the extensional stresses of the Tepic-Zacoalco rift. The changes in seismic patterns and obtained focal mechanisms are consistent with observed fluid effects at many geothermal sites worldwide, but also could suggest resumption of activity at this currently dormant volcano. (c) 2021 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).

To study the seismic characteristics of the tectonic borders of the Rivera, Pacific, Cocos and North America Plates, we undertook the TsuJal Project, a passive seafloor seismic project conducted from April to November 2016.In addition to the Jalisco Seismic Network, ten 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 www.videleaf.comstates 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.

An important unresolved question about the crustal structure around the Islas Marías Archipelago is where the Rivera-North American plate subduction ends and the Tamayo fracture zone begins, from SE to NW.It is now clear that Sierra de Cleofas and the Islas Marías Escarpment comprise the northwestern continuation of the Middle America trench from results of the www.videleaf.comTsuJal project, which have shed light on the northwesternmost part of the Jalisco block structure.However, other questions remain.In this chapter, we analyze 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, wideangle 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.In this region, 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 were characterized.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.

EDITORIAL article Front. Earth Sci., 25 March 2022Sec. Solid Earth Geophysics https://doi.org/10.3389/feart.2022.852059

Ceboruco Volcano is a Quaternary stratovolcano located in Nayarit near the Trans-Mexican Volcanic Belt western limit. It is one of the most active in the region and the only volcano in Nayarit with historically documented eruptions, the last one between 1870 and 1875. Currently, seismicity and fumarolic activity suggest hydrothermal activity. To study the geoelectrical setting at Ceboruco Volcano and its hydrothermal system, a magnetotelluric exploration campaign was carried out in November 2016, establishing 24 measuring stations at the caldera, and foothills of the volcanic edifice. Three broadband instruments were used in the sampling frequency range of 32,768–128 Hz. Recorded time series were processed to determine the MT transfer functions using a robust algorithm and consider the remote-reference station technique. Dimensionality analysis based on the phase tensor determined a shallow 1D geoelectrical structure at periods shorter than 1 s, while a 3D formation was defined at longer periods. To approximate the Ceboruco Volcano substructure, the 3D inversion of magnetotelluric data was carried out. 3D modeling revealed surficial resistivity regions that were related to young volcanic deposits. A relative conductor (10–30 Ωm) was also associated with the shallow regional aquifer. The two most intriguing results of 3D inversion were one uppermost conductive region (~1 Ωm) that established characteristics, resistivity, position, and thickness related to a clay alteration minerals zone. The other one (2–5 Ωm) corresponds to a conductive area broadening and fading with depth, centered slightly to the west of the summit at Ceboruco Volcano. The preferred interpretation of this geoelectrical feature was an envelope of high-temperature fluids, convection of steam, and brines, and they are interacting with the host-rock and surficial groundwater. This geoelectrical feature extends in depth, suggesting a permeable region at the Trans-Mexican Volcanic Belt basement that may be targeted for in-depth geothermal exploration. The geoelectrical setting identified in this study provides information that contributes to reducing uncertainty about the geological, geophysical, and hydrogeological conceptual models at Ceboruco Volcano geothermal system.

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.

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 Jalisco region in western Mexico is one of the most seismically active in the country. The city of Puerto Vallarta is located at Bahía de Banderas on the northern coast of Jalisco. Currently there exists a Seismic Gap in the Northern coast of Jalisco (Vallarta Gap). Historically seismogenic tsunamis have affected the coast of Jalisco. In this work, we assess the risk due to a local tsunami in the city of Puerto Vallarta as a function of the interaction between hazard and vulnerability. We model the tsunami hazard, generation and propagation, using the initial conditions for a great earthquake (Mw ≥ 8.0) similar to those that occurred in 1787 at Oaxaca and in 1995 at Tenacatita Bay, Jalisco. Vulnerability is estimated with available data for the years 2010–2015 with sociodemographic variables and the location of government, commercial or cultural facilities. The area with the highest vulnerability and risk is between the valleys of the Ameca and Pitillal Rivers, extending to a distance greater than 5.1 km from the coastline and affecting an area of 30.55 km2. This study does not consider the direct damage caused by the tsunamigenic earthquake and aftershocks; it assumes that critical buildings in the region, mostly hotels, would not collapse after the earthquake and could serve as a refuge for its users. The first (It) tsunami wave arrives to Puerto Vallarta (Cuale) 19 min after the earthquake with a height (Hi) of 3.7 m; the run-up (At) arrives 74 min after earthquake with a height (Hr) of 5.6 m.

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.

Historically, the city of Guadalajara has been affected not only by great regional earthquakes (M > 7.0) associated with the subduction process and regional crustal structures but also by local seismic sequences, that caused moderate to severe structural damage to buildings, whose source is not clear. Between December 2015 and May 2016, two seismic sequences occurred, affecting the city of Guadalajara. Both seismic sequences were recorded by the Jalisco Seismic Accelerometric Telemetric Network. The preliminary locations for May 2016 sequence estimated by the Antelope automatic system show alignment with an NNE-SSW trend, west of the city of Guadalajara. The subsequent relocations of theses earthquakes show two N-S alignments at the west of the city of Guadalajara, which agree with December 2015 hypocenters. The focal mechanisms analysis of the earthquakes shows that most of them correspond to normal fault mechanisms that are parallel to the hypocentral alignments suggesting the existence of two active faults responsible for the seismic sequences. Furthermore, these structures might constitute a graben, which we refer to as Zapopan Graben. Additionally, we calculated that these faults are 21 and 28 km length, respectively, which indicates that could have the potential to generate shallow earthquakes that reach magnitudes of 6.2 and 6.5, and could cause significant damages in the Guadalajara Metropolitan Zone.