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| Casma Fault | |
|---|---|
| Name | Casma Fault |
| Location | Ancash Region, Peru |
| Coordinates | 9°S 78°W (approx.) |
| Type | Strike-slip, oblique-slip |
| Length | ~120 km |
| Plate | Nazca Plate, South American Plate |
| Status | Active |
| Notable earthquakes | 20th–21st century seismicity |
Casma Fault is a major active fault zone in the Ancash Region of Peru running along the western edge of the Andean orogeny near the coastal basin. The fault lies within the convergent margin between the Nazca Plate and the South American Plate, interacting with regional structures such as the Cordillera Blanca Fault System, the Casma River, and the coastal basins near Chimbote and Huarmey. Research on the fault connects studies from institutions like the Geological Society of America, the Peruvian Geological Survey, and international teams from University of California, University of Tokyo, and Institut de Physique du Globe de Paris.
The fault transects Mesozoic and Cenozoic sedimentary sequences, volcanic units, and metamorphic basement of the western Andes Mountains, juxtaposing Early Cretaceous strata, Paleogene marine sediments, and Neogene continental deposits near the Casma Basin, Santa River Basin, and the structural domain of the Cordillera Negra. Associated rock units include limestones correlated with the Paracas Formation, tuffs similar to the Pisco Formation, and intrusive bodies akin to those described in the Cordillera Blanca Batholith. Regional mapping by teams linked to the Smithsonian Institution and the US Geological Survey integrates stratigraphic correlations from coastal outcrops at Huaraz and offshore seismic profiles near Paracas.
Situated at the active convergent margin where the Nazca Plate subducts beneath the South American Plate, the fault is part of a network of forearc and upper-plate structures that includes the west-verging thrusts of the Andean orogeny, the oblique-slip transcurrent systems documented across Peru, and block-bounding faults like those in the Ancash Region. Plate kinematic models developed by groups at Scripps Institution of Oceanography, Institut Français de Recherche pour l'Exploitation de la Mer, and Universidad Nacional Mayor de San Marcos show partitioning of oblique convergence into trench-parallel shear and trench-normal shortening that localizes slip on strike-slip faults such as this one and on nearby reverse faults documented in studies from Cambridge University and ETH Zurich.
The fault exhibits dominantly right-lateral strike-slip motion with components of reverse dip-slip recorded in offset terraces, folded strata and pressure-solution features in carbonate horizons. Field observations record en-echelon fault segments, pull-apart basins comparable to those in the San Andreas Fault systems, and restraining bends akin to structures mapped near Antofagasta and Iquique. Structural analyses conducted by teams from Imperial College London and University of Buenos Aires describe a segmented trace with strike changes, splay faults, and linking transfer zones that control rupture propagation and localize damage zones visible in exposures near Huaylas and coastal cliffs by Chimbote.
Instrumental seismicity recorded by networks operated by Instituto Geofísico del Perú, USGS, and regional observatories documents microseismicity, moderate earthquakes, and regional rupture interactions with megathrust events like those cataloged for the 1868 Arica earthquake and the 1970 Ancash earthquake. Historical accounts from colonial archives in Lima and reports compiled by the Peruvian Navy and researchers at Monash University provide constraints on felt reports and coastal damage that implicate upper-plate faulting episodes. Geodetic campaigns by NASA and ESA using GPS and InSAR data detect interseismic strain accumulation and transient deformation correlated with episodic slip on the fault and nearby structures.
Trenches excavated across Holocene terraces, radiocarbon ages from lacustrine deposits near the Casma River and cosmogenic nuclide analyses by teams at Carnegie Institution for Science yield estimates of late Quaternary slip rates on the order of millimeters per year, with recurrence intervals constrained to centuries for large ruptures. Paleoseismic records compared with those from the Quito Fault and the Nazca Ridge-influenced margin indicate segmentation in rupture behavior and variable slip per event. Collaborative studies with University of Washington and University of Arizona integrate stratigraphic offsets, fault scarp degradation models, and luminescence dating to refine a chronology of Holocene earthquakes.
The fault scarp, offset fluvial terraces, linear valleys, shutter ridges, and sag ponds along the coastal forearc are geomorphic markers cited in geomorphology surveys by National Geographic Society-supported projects and mapping by Peruvian Ministry of Culture teams near archaeological sites such as those in the Casma-Chimbote corridor. Coastal cliffs and submarine canyons offshore show morphologic expressions tied to fault-controlled uplift and subsidence comparable to observations near Ica and Tumbes. Remote sensing campaigns using imagery from Landsat, Sentinel-1, and aerial LiDAR collected by Jet Propulsion Laboratory reveal subtle coseismic offsets, knickpoints, and drainage reorganizations attributable to the fault.
Seismic hazard associated with the fault affects population centers including Chimbote, Casma, and agricultural valleys that support fisheries linked to the Humboldt Current and export commodities routed through ports monitored by the Peruvian Port Authority. Infrastructure risks involve highways, pipelines, and the Central Highway corridor as assessed by engineering teams at Pontifical Catholic University of Peru and Universidad Nacional de Ingeniería. Environmental consequences include changes to groundwater regimes in the Casma Valley, coastal erosion impacting mangrove and marine reserves noted by World Wildlife Fund and CONAMA studies, and implications for cultural heritage sites under the purview of UNESCO-linked preservation initiatives.
Category:Geology of Peru Category:Seismic faults of South America