Sur-Nacimiento Fault

Sur-Nacimiento Fault
Name	Sur-Nacimiento Fault
Location	Central Chile, Maule Region
Length	~85 km
Type	Oblique-slip (reverse + strike-slip)
Dip	Northeast-dipping
Displacement	Holocene slip documented
Status	Active

Sur-Nacimiento Fault is an active oblique-slip fault system in central Chile within the Maule Region, accommodating deformation related to the interplay of the Nazca Plate, South American Plate, and intraplate structures such as the Coastal Cordillera and the Andes. The fault links crustal shortening and lateral shear between prominent regional structures including the Liquiñe-Ofqui Fault Zone, the Atacama Fault Zone, and the Chilean subduction margin, and has been implicated in continental seismicity and landscape evolution recorded across the Central Chilean Depression and adjacent ranges.

Geology and Tectonic Setting

The Sur-Nacimiento Fault lies within a convergent margin context dominated by the subduction of the Nazca Plate beneath the South American Plate at the Chilean trench near Concepción, Chile and Valparaíso. Regional tectonics are influenced by segmentation of the trench near the 2007 Tocopilla earthquake rupture zones and coupling variations observed since the 1960 Valdivia earthquake and the 2010 Maule earthquake. The fault system strikes roughly NW-SE, cutting metamorphic and plutonic terranes related to the Coastal Batholith of central Chile, Tertiary sedimentary basins such as the Colbún Basin, and Quaternary volcanic centers including Llaima Volcano and the Villarrica Complex. Structural relations show linkage with forearc fault networks mapped alongside the Chile Triple Junction and back-arc shortening near the Altiplano-Puna plateau margins.

Fault Geometry and Kinematics

Mapped geometry reveals a multi-segmented trace with steep northeast-dipping planes that produce reverse motion together with dextral strike-slip components; these kinematics are comparable to oblique thrusts documented on the North Chile Ridge margin and reverse-slip faults in the Andean orogeny. Geophysical profiles integrating seismic reflection across sections near Rancagua and Talca indicate crustal-scale ramps and imbricate thrusts similar to structures imaged beneath Santiago, Chile. Focal mechanisms from local networks align with thrust-dominated solutions reported for the Chilean seismic gap and show centroid depths compatible with the brittle-ductile transition beneath the Cordillera de la Costa.

Seismicity and Earthquake History

Instrumental seismicity includes moderate earthquakes recorded by the National Seismological Center (Chile), the US Geological Survey, and regional observatories in Concepción and Valdivia. Historical earthquakes affecting the zone are temporally correlated with ruptures on neighboring faults implicated in seismic sequences observed during the 19th century Chile earthquakes and linkage to larger events such as the 2010 Chile earthquake. Paleodamage and accounts in archives from Santiago and Talca hint at episodic ground shaking consistent with multi-segment ruptures similar to events documented along the Pichilemu Fault and the Arauco Peninsula.

Paleoseismology and Slip Rate

Trench investigations in alluvial fans and colluvial deposits across the fault have produced stratigraphic offsets dated by radiocarbon from sites near Nacimiento and Constitución, yielding late Holocene event horizons comparable to slip rates measured on other Chilean faults like the Cauquenes Fault. Cosmogenic exposure dating and optically stimulated luminescence studies correlated to terraces along the Bío Bío River and Maule River suggest recurrent surface-rupturing earthquakes with recurrence intervals comparable to estimates for the Lonquimay and Los Tuxtlas sectors of the margin. Slip-rate estimates span the lower millimeters per year, consistent with partitioning of trench-parallel and trench-normal strain known from models of the Andean shortening.

Geomorphic Expression and Surface Rupture

The Sur-Nacimiento Fault is expressed by linear escarpments, shutter ridges, deflected drainages, and offset moraines across the Central Valley (Chile) landscape. Fluvial terraces, piedmont fans, and glacial deposits show cumulative displacements analogous to morphologies mapped near Puerto Montt and Osorno. Surface ruptures preserved in fan deposits record both vertical uplift and lateral offsets similar to patterns documented for the Liquiñe Fault and active scarps in the Pacific Ring of Fire provinces of Chile.

Hazard Assessment and Risk Mitigation

Hazard models combining fault slip-rate, paleoseismic recurrence, and regional seismic coupling inform seismic hazard maps produced by Chilean agencies and international partners like the Global Earthquake Model (GEM) consortium. Urban centers including Concepción, Talca, and infrastructure corridors such as the Pan-American Highway and transmission lines are evaluated for shaking intensity, landslide initiation, and tsunami potential where coastal segments interact with slope failures near Bahía de Concepción. Risk mitigation actions prioritize building-code updates informed by the Ministerio de Obras Públicas (Chile), retrofitting of lifeline structures, and community preparedness programs implemented with agencies like the ONEMI and international bodies including the World Bank.

Research and Monitoring efforts

Ongoing research incorporates dense seismic networks operated by the University of Chile, satellite geodesy from European Space Agency missions and NASA platforms using InSAR to resolve slow slip and interseismic deformation, and geologic mapping coordinated with the Servicio Nacional de Geología y Minería (Sernageomin). Collaborative projects involve universities such as the Pontifical Catholic University of Chile, the University of Concepción, and international institutions including the Lamont–Doherty Earth Observatory and the GEOMAR Helmholtz Centre for Ocean Research Kiel. Future monitoring priorities emphasize expanded GPS arrays, paleoseismic trenching, and multi-disciplinary studies linking volcanism, hydrology, and seismic hazard analogous to integrated programs undertaken after the 2010 Maule earthquake and the 1960 Valdivia earthquake.

Category:Seismic faults of Chile Category:Geology of Maule Region