Seismic structure of the southern Rivera plate and Jalisco block subduction zone

Structural and tectonic features in the Pacific Coast of Mexico generate a high level of seismic activity in the Jalisco block (JB) region, making it one of the most attractive areas of the world for geophysical investigations. The Rivera North America contact zone has been the object of different tectonic studies in recent years framed within the TsuJal project. To this day, this project is generating numerous crucial geophysical results, which significantly improve our understanding of the region. Our study is focused on the interaction between the south of the JB and Rivera plate (RP), which crosses the Middle America trench. We also cover an offshore onshore transect of 130 km length between the eastern Rivera fracture zone and La Huerta region, in the Jalisco state. To characterize this region,we interpreted wide angle seismic, multichannel seismic, and multibeam bathymetry data. The integration of these results, with the local and regional seismicity recorded by the Jalisco Seismic Accelerometric Telemetric Network and by the Mapping the Rivera Subduction Zone experiment, provides new insights into the geometry of the southern RP, which is dipping 12 14 degrees under the JB in the northeast southwest direction. Moreover, our results provide new seismic images of the accretionary wedge, the shallow crust, the deep crust, and the upper-mantle structure along this profile.Comment: Seismological Research Letters 201

Seismic energy attenuation in the region between the coast of Guerrero and Mexico City: differences between paths along and perpendicular to the coast

Attenuation of seismic energy in Central Mexico from earthquakes generated along the South Coast has been discussed in several works. The attenuation interpretations falls broadly in two categories: the first, lower attenuation in paths going inland relative to paths going along the Coas

New insights into the subducting oceanic crust in the Middle American trench off western Mexico (17-19°N)

We present new multibeam bathymetric and multichannel seismic data on the Middle American Trench, between 17 and 19°N. These data show, north of the present tip of the East Pacific Rise, unsedimented seafloor with an abyssal hill fabric bare of sediments at the outer wall of the trench (18°30'N). Two multichannel seismic profiles orthogonal to the Middle American Trench display clear oceanic crust extending more than 20 km beneath the overriding plate. These seismic images suggest that the subducting oceanic crust along the Middle American Trench is younger than previously proposed. This result, therefore, implies a new location for the East Pacific Rise termination in relation to the trench. The subduction of this young oceanic crust off western Mexico provides new constraints on the deformation and magnetism of the western Mexican mainland. (Résumé d'auteur

S wave attenuation in the coastal region of Jalisco-Colima, Mexico

Aftershock data from the October 9, 1995, M = 7.6 earthquake, that occurred in the coastal subduction region of Colima-Jalisco, Mexico, are used to obtain estimates of the frequency independent quality factor Q(s) and spectral decay parameter κ, in the approximate frequency range 3 Hz ≤ f ≤ 40 Hz, as functions of hypocentral distance r. A regression analysis results in the relations for S waves: Q(s) = 261.397 + 3.198r ± 15.536 κ = 0.009651 + 0.000462r ± 0.0012. The observed distance dependence of Q(s) and κ is similar to that reported for the Mexican regions of Oaxaca and Guerrero. Our Q(s) values agree with those reported for Oaxaca and northern Baja CA for frequencies around 8 Hz, and are somewhat lower (a factor of ~0.8 to ~0.5) for higher frequencies around 20 Hz; however, they are siginificantly lower than all but the lowest values reported for the Guerrero region, attaining factors ~ 0.25 and ~ 0.13 for frequency ranges around 8 and 20 Hz, respectively. It thus appears that the Guerrero region has an anomalously low attenuation compared with the flanking coastal regions of Oaxaca-Chiapas to the SE and Jalisco-Colima to the NW

Accelerated surgery versus standard care in hip fracture (HIP ATTACK) : an international, randomised, controlled trial

Background: Observational studies have suggested that accelerated surgery is associated with improved outcomes in patients with a hip fracture. The HIP ATTACK trial assessed whether accelerated surgery could reduce mortality and major complications. Methods: HIP ATTACK was an international, randomised, controlled trial done at 69 hospitals in 17 countries. Patients with a hip fracture that required surgery and were aged 45 years or older were eligible. Research personnel randomly assigned patients (1:1) through a central computerised randomisation system using randomly varying block sizes to either accelerated surgery (goal of surgery within 6 h of diagnosis) or standard care. The coprimary outcomes were mortality and a composite of major complications (ie, mortality and non-fatal myocardial infarction, stroke, venous thromboembolism, sepsis, pneumonia, life-threatening bleeding, and major bleeding) at 90 days after randomisation. Patients, health-care providers, and study staff were aware of treatment assignment, but outcome adjudicators were masked to treatment allocation. Patients were analysed according to the intention-to-treat principle. This study is registered at ClinicalTrials.gov (NCT02027896). Findings: Between March 14, 2014, and May 24, 2019, 27 701 patients were screened, of whom 7780 were eligible. 2970 of these were enrolled and randomly assigned to receive accelerated surgery (n=1487) or standard care (n=1483). The median time from hip fracture diagnosis to surgery was 6 h (IQR 4\u20139) in the accelerated-surgery group and 24 h (10\u201342) in the standard-care group (p<0\ub70001). 140 (9%) patients assigned to accelerated surgery and 154 (10%) assigned to standard care died, with a hazard ratio (HR) of 0\ub791 (95% CI 0\ub772 to 1\ub714) and absolute risk reduction (ARR) of 1% ( 121 to 3; p=0\ub740). Major complications occurred in 321 (22%) patients assigned to accelerated surgery and 331 (22%) assigned to standard care, with an HR of 0\ub797 (0\ub783 to 1\ub713) and an ARR of 1% ( 122 to 4; p=0\ub771). Interpretation: Among patients with a hip fracture, accelerated surgery did not significantly lower the risk of mortality or a composite of major complications compared with standard care. Funding: Canadian Institutes of Health Research