Revista de la Asociación Geológica Argentina

Assessment of Primary and Secondary Environmental Effects of the 23 November 1977 San Juan Earthquake (Mw 7.4), Argentina, Using the Environmental Seismic Intensity Scale (ESI-2007)

Laura Perucca, Silvia Beatriz Palacios, Alejandro Oro — Mon, 30 Mar 2026 00:00:00 +0000

This study analyzes the environmental effects generated by the November 23, 1977 earthquake (Mw 7.4), whose epicenter was located in the province of San Juan, with the aim of estimating its intensity using the Environmental Seismic Intensity Scale (ESI-2007). Information from newspapers, technical reports, and scientific publications was integrated to build a detailed database of the primary and secondary effects associated with the event. The ESI-2007 methodology allowed us to delineate the most affected areas and characterize the distribution and magnitude of the observed processes. Numerous effects were documented, including the surface rupture of the Niquizanga Fault, soil liquefaction, fissures, lateral spreading, subsidence, landslides, rockfalls, and hydrological anomalies. Primary effects were concentrated along the southeastern margin of the Pie de Palo range, whereas secondary effects extended broadly across the Tulum Valley, the Bermejo Valley, and sectors of northern Mendoza. This work highlights the usefulness of the ESI-2007 scale for assessing historical earthquakes in low-population regions and provides relevant information for land-use planning and seismic-hazard mitigation.

Basalts of the west of La Pampa Province and their role in the regional hydrological system

MAURO Bernardi — Mon, 30 Mar 2026 00:00:00 +0000

Western La Pampa province is partially covered
by pahoehoe basaltic flows derived from the Neogene-Quaternary Payenia volcanic fields, in southern Mendoza province. These lava flows comprise simple or compound flows, each with vesicular flow tops and basal zones, with intervening massive interiors, and are affected by fractures of both primary (columnar jointing and inflation-related features) and secondary (weathering) origin. The external and internal drainage patterns and hydraulic properties of these lithologies vary locally as a function of: 1) fracture and structural characteristics (density, connectivity, orientation, aperture, and persistence); 2) vesicularity and the distribution of other cavities; and
3) topographic controls, among other factors. Collectively, these features exert a strong control on infiltration, subsurface flow, storage, and discharge within the regional hydrological system. Petrophysical analyses of vesicular basalt samples showed low intrinsic permeabilities, with corresponding hydraulic conductivity values significantly lower than those reported for basalts in other regions. In contrast, the equivalent hydraulic conductivity estimates derived from the cubic law for fracture flow are up to three orders of magnitude higher than previously reported values for this lithology. These results indicate that groundwater recharge and flow are primarily controlled by fracture networks rather than by primary vesicular porosity. The low regional topographic gradient of the basalt-covered area, together with the presence of a clastic cover, enhances water retention and reduces surface runoff.

Differential erosion of cliffs and wave-cut platforms in Mar del Plata, Argentina

Federico Isla, Marcia MOJICA, Jorge GUTIERREZ — Tue, 26 May 2026 00:00:00 +0000

Cliff retreat and abrasion platform erosion are natural
processes that exhibit significant spatial and temporal variability. Both features characterize the southern coast of Mar del Plata (Argentina)
and have undergone changes driven by the magnitude and recurrence of storm events, as well as by anthropogenic factors such as the past sand extraction, the management of coastal resort infrastructure, and inadequately implemented coastal defense works. These factors are further compounded by future impacts associated with climate change, particularly those linked to anthropogenic sea-level rise. Local variability is also controlled by lithological resistance and its vertical and lateral distribution along the coast. The cliffs and abrasion platforms are primarily composed of loessic silts containing calcrete (tosca) horizons, which locally enhance resistance. Where the coastline is formed by more resistant quartzites, these units develop prominent headlands that bound pocket beaches. At smaller scales, erosion may be influenced by water excess and infiltration processes, including runoff and percolation through fractures. Additionally, benthic organisms play a dual role, contributing either to the bioerosion of abrasion platforms or to their
stabilization through biogenic armoring.

Sismitas cuaternarias de la Cuenca del Golfo San Jorge, Patagonia, Argentina

Mon, 30 Mar 2026 00:00:00 +0000

Este estudio caracteriza estructuras de deformación en sedimento blando en depósitos cuaternarios alrededor de Comodoro Rivadavia, Chubut, Argentina. La sucesión comprende una sección inferior marina costera, una sección media fluvial y una sección superior marina costera. Las estructuras de deformación se desarrollan en intervalos estratigráficos de 0,6 a 3 m y se agrupan en cuatro eventos de deformación: tres en la sección inferior y uno en la sección superior. El evento 2 proporciona la correlación estratigráfica más robusta entre las localidades estudiadas, separadas por ~10 km, mientras que el evento 4 se reconoce en ambas localidades, pero consiste en estructuras de deformación discontinuas y aisladas. Las estructuras de deformación frágil incluyen fallas normales mesoscópicas sinsedimentarias, con geometrías
planares, rotacionales o no rotacionales, y rumbos NO-SE a NE-SO. Las estructuras de escape de fluido incluyen pilares y laminación convoluta, mientras que las estructuras de deformación dúctil comprenden pliegues en cajón y recumbentes. Este conjunto de estructuras es compatible con deformación en sedimentos saturados en agua, incluyendo procesos de licuefacción y fluidización. El evento 2 se interpreta como candidato más robusto asociado a sacudidas sísmicas, debido a su continuidad lateral, correlación entre localidades distantes, confinamiento en un horizonte estratigráfico discreto limitado por estratos no deformados y presencia de fallas normales sinsedimentarias. Estos resultados aportan evidencia de deformación en sedimentos blandos en depósitos cuaternarios de la Patagonia extraandina y contribuyen a la discusión sobre la actividad neotectónica a lo largo del flanco norte de la Cuenca del Golfo San Jorge.

Obituario Luis Antonio Spalletti

Carlos Limarino, Carlos W. Rapela — Mon, 30 Mar 2026 00:00:00 +0000

No corresponde