María Teresa Ramírez-Herrera

Geomorphic assessment of active tectonics in the Acambay graben, Mexican Volcanic Belt

Spatial variations of Quaternary deformation and tectonic activity of faults along the Acambay graben are assessed using geomorphic and morphometric approaches. The Acambay graben is an east–west trending structure of apparent Quaternary age, located in the central part of the Mexican Volcanic Belt, which gives rise to pronounced scarps over a distance of about 80 km. Continuing tectonic activity in the Acambay graben is confirmed by recent well documented seismic episodes. The intensity of active tectonics has been interpreted through a detailed geomorphic study of the fault-generated mountain fronts and fluvial systems. The combined geomorphic and morphometric data provide evidence for relative variations in tectonic activity among the Acambay graben faults. Geomorphic indices suggest a relatively high degree of tectonic activity along the Venta de Bravo and the Acambay–Tixmadeje faults, followed, in order of decreasing activity, by the Pastores, Temascalcingo and Tepuxtepec faults. Spatial variations within faults have also been identified, suggesting a higher level of tectonic activity at the tips of the faults. This pattern of variation in the relative degree of tectonic activity is consistent with field evidence and seismic data for the Acambay graben. Geomorphic evaluation of the Acambay graben faults suggests that the Acambay–Tixmadeje and Venta de Bravo faults, and specifically the tips of these faults and a central segment near the town of Venta de Bravo, should be considered as areas of potentially high earthquake risk.

Unearthing earthquakes and their tsunamis using multiple proxies: the 22 June 1932 event and a probable fourteenth-century predecessor on the Pacific coast of Mexico

Tsunami deposits have been widely studied in temperate latitudes, but the intrinsic difficulties associated with tropical coastal environments, and the intensity of bioturbation in these habitats, limit the possibilities of analysing these formations. Here, we investigate the deposits on the Colima coast of Mexico, which overlies the subducting Rivera and Cocos Plates, in order to reconstruct the tsunami inundation history and related hazard. We developed a multi-proxy study aimed to recognize and date historical and palaeotsunami deposits, including historical data on the effects of a known tsunami, geomorphological mapping, stratigraphic, grain size, organic matter content, diatoms, geochemical composition, magnetic susceptibility, and anisotropy of magnetic susceptibility, together with radiometric dating (210Pb and 14C). We identified two probable tsunami deposits at Palo Verde estuary including a historical event associated with the Mw 6.9 earthquake on 22 June 1932 and a palaeotsunami most likely generated by a similar event in the fourteenth century. This work shows that it is possible to identify both historical and palaeotsunamis in the tropical environment of Mexico’s Pacific coast. These data will serve to enhance our understanding of tsunami deposits in tropical environments and of the regional tsunami hazard.

Magnetic record of extreme marine inundation events at Las Salinas site, Jalisco, Mexican Pacific coast

Abstract Extreme marine inundation events (i.e. severe storms and tsunamis) denote a major hazard to coastal communities around the globe. In order to assess this hazard, long-term (beyond the instrumental and historic records) information on the magnitude and frequency of these events is critical. The coastal sedimentary record, together with other proxies, is now being tested to distinguish and reconstruct evidence of ancient inundation events. Recent studies commonly use anisotropy of magnetic susceptibility (AMS) parameters without statistical evaluation of the lateral variability of sedimentary layers. Here, we provide results from tested sedimentary layers. Moreover, we discuss the most recent strategies to identify deposits produced by major inundation events using the full battery of rock magnetic properties of sediments in Careyes Bay on the Jalisco coast, Eastern Pacific, a tectonically active coast subject to hurricanes. Oriented samples of lagoonal sediments were taken from a dug pit at Las Salinas site. The sampled stratigraphic sequence was basically composed of an upper sand and lower clay units. The upper part of the Las Salinas profile shows a drop in magnetic susceptibility by 50%. Two distinct magnetic fabrics are clearly identified. Fabric from the upper part of the profile most probably reflects a sedimentary structure which was originated in a more dynamic environment than the magnetic fabric recognized in the lower part of the profile. Hysteresis parameters also show variation in behaviour between the upper and lower parts of the profile. We propose here that the origin of the upper sand unit at the study site is most probably related to an extreme marine inundation event.

Landslide manual and automated inventories, and susceptibility mapping using LIDAR in the forested mountains of Guerrero, Mexico

ABSTRACT Landslides are a pervasive natural disaster, resulting in severe social, environmental and economic impacts worldwide. The tropical, mountainous landscape in South-West Mexico is predisposed to landslides because of frequent hurricanes and earthquakes. The main goal of this study is to compare landslide susceptibility maps in Guerrero derived using high-resolution LIDAR (light detection and ranging) data from both a manual landslide event inventory and an automated landslide inventorying algorithm. The paper also highlights the importance of applying LIDAR data in landslide inventorying and susceptibility mapping. We mapped landslides based on two approaches: (1) manual mapping using satellite images and (2) automatic identification of landslide morphology employing the Contour Connection Method (CCM). We produced a landslide susceptibility map by computing the probability of landslide occurrence from statistical relationships of inventoried landslides detected with LIDAR digital terrain models (DTMs) and derived landslide-causing factors using the logistic regression method. Our results suggest that the automated inventory derived through the CCM algorithm with LIDAR DTMs effectively minimizes the time-consuming and subjective manual inventorying process. The high overall prediction accuracy (up to 0.83) from logistic regression demonstrates the validity and applicability deriving reliable landslide susceptibility maps from an automated inventory; however, LIDAR data are required.

Evidencias ambientales de cambios de nivel de la costa del Pacífico de México: terremotos y tsunamis

The study of prehistoric earthquakes and tsunamis using environmental evidence of coastal level changes, where sudden changes from terrestrial to marine envi...

Relating the long-term and short-term vertical deformation across a transect of the forearc in the central Mexican subduction zone

Author(s): Ramirez-Herrera, MT; Gaidzik, K; Forman, S; Kostoglodov, V; Burgmann, R; Johnson, CW | Abstract:

Updated Tsunami Catalog for the Jalisco‐Colima Coast, Mexico, Using Data from Historical Archives

ABSTRACT Modern earthquakes and tsunamis catalogs available online are compilations of earlier catalogs that included some inaccurate information. Here, we present a thorough revision of tsunamigenic earthquakes that, in historical time, have affected the Mexican Pacific coast between Jalisco and Colima. This area is located in a complex tectonic setting where the Rivera–Cocos and North American plates have produced four M ≥8 earthquakes and two big tsunamis since the nineteenth century. We identified tsunamigenic earthquakes that were not previously documented in modern earthquake and tsunami catalogs available online through a careful reading of original historical archives and documents. Our results indicate the occurrence of 21 events; among those we report 2 earthquakes documented for the first time (1563 and 1816) for the Jalisco‐Colima coast, and 8 large or medium intensity tsunamis also first reported (1816, 1818, 1900 [two tsunamis], 1911, 1933 [two tsunamis], and 1941) through documentary evidence. Our results demonstrate the need for a thorough investigation of historical documents and geological evidence of earthquakes and their tsunamis to accurately assess seismic and tsunami hazard.

La Pintada landslide—A complex double-staged extreme event, Guerrero, Mexico

Abstract Extreme storms commonly trigger landslides in regions of humid, warm tropical climate causing loss of life and economic devastation. The tropical mountainous areas of Guerrero in southwest Mexico are frequently hit by extreme hurricanes and cyclones and thus prone to landslides. On 16 September 2013, a huge landslide resulted in 71 fatalities and destroyed a large part of La Pintada Village. We applied remote sensing techniques using the LIDAR DEM and high-resolution images of the La Pintada area, a post-landslide field survey, geotechnical laboratory tests of colluvium material from the landslide, and a slope stability analysis. We also interviewed eyewitnesses accounts of the event. Our results suggest that the 2013 La Pintada landslide was a complex and two-stage event. An intense four-day-long rainfall event related to the landfall of Hurricane Manuel resulted in the oversaturation of soil, which was the main factor that caused the landslide. The effect of rainfall was amplified by the lack of high and dense vegetation on the 250-m-high slope. The lack of vegetation and slope-under-cutting likely contributed to the decreased slope stability. We suggest that increased intensity of extreme storms has contributed to increased landslides in this area. Furthermore, in tropical climate areas, where significant population lives in mostly developing countries, the combination of these phenomena makes them highly vulnerable to extreme storms and landslide hazards.