Guerrero seismic gap

Guerrero seismic gap
Name	Guerrero seismic gap
Location	Guerrero, Mexico
Coordinates	17°N, 101°W
Plate boundary	Cocos Plate–North American Plate subduction zone
Length	200–300 km
Slip rate	4–8 mm/yr
Last major event	1911 (partial rupture)
Status	Seismic gap

Guerrero seismic gap

The Guerrero seismic gap is a persistent segment of the Middle America Trench subduction interface off the coast of Guerrero and southern Michoacán known for accumulated strain and a deficit of recent large earthquakes. It forms a conspicuous gap between ruptured segments associated with historic earthquakes near Acapulco, Oaxaca, and Colima and is a focal point for studies by institutions such as the Servicio Sismológico Nacional (Mexico), the United States Geological Survey, and the International Seismological Centre.

Overview and definition

The term denotes a locked portion of the megathrust where interseismic coupling produces long-term elastic strain that has not been released by recent magnitude 7–8 earthquakes. The feature lies downdip of the coastal forearc that includes the Guerrero coast, the Mexican Volcanic Belt, and the accretionary prism offshore. It is defined thermally and mechanically: a shallower, highly coupled patch overlain by the seismogenic plate interface where the Cocos Plate meets the North American Plate. The seismic-gap concept traces to studies of rupture segmentation applied by researchers at the California Institute of Technology and the Massachusetts Institute of Technology and has been applied in operational risk communication by the Centro de Instrumentación y Registro Sísmico (CIRES).

Tectonic setting and seismic history

The regional tectonics are dominated by east-northeast subduction of the Cocos Plate beneath the North American Plate along the Middle America Trench. Convergence rates derived from GPS and marine geodesy studies by teams at UNAM and the Jet Propulsion Laboratory indicate trench-normal motion of approximately 4–8 mm/yr. Historical seismicity catalogs show large ruptures in adjacent segments: the 1911 Guerrero–Oaxaca events, the 1985 Mexico City earthquake (rupture further east), and recurrent tsunamigenic events affecting the Pacific coast near Jalisco and Colima. Paleoseismological and coral uplift studies led by groups at the University of California, Santa Cruz and the Instituto de Geofísica (UNAM) have extended the record using stratigraphic and radiocarbon evidence to identify prior megathrust earthquakes and slow-slip activity.

Characteristics and seismic hazard

The gap is characterized by a locked zone roughly 200–300 km long and tens of kilometers wide with high interseismic coupling measured by GPS networks operated by UNAM, the Servicio Sismológico Nacional (Mexico), and international collaborations. Superimposed on the locked patch are episodic slow slip events (SSEs) and non-volcanic tremor (NVT) recorded by dense arrays deployed by teams from the Instituto de Geofísica (UNAM), the Earth Observatory of Japan, and the Geological Survey of Canada. These transient phenomena alter stress transfer and seismic hazard on timescales from months to decades, complicating probabilistic seismic hazard assessments by organizations such as the Global Seismographic Network partners and regional civil protection agencies like Protección Civil (Mexico). Ground-motion modeling for megathrust rupture scenarios has been produced by consortia involving USGS and Mexican institutions to estimate shaking in Mexico City, Acapulco, and inland cities.

Monitoring and research

Monitoring combines land-based GPS networks, broadband seismometers from the Centro de Instrumentación y Registro Sísmico (CIRES), ocean-bottom seismometer campaigns coordinated with the Woods Hole Oceanographic Institution, and seismic reflection surveys by marine geology groups at the National Autonomous University of Mexico (UNAM). Research has focused on the interaction of SSEs, NVT, and locked asperities, with notable contributions from the Earthquake Research Institute (University of Tokyo) and the Scripps Institution of Oceanography. Seafloor geodetic experiments supported by the National Science Foundation and the European Research Council have begun to resolve interplate deformation offshore. Numerical modeling teams at the California Institute of Technology, École normale supérieure, and Imperial College London have simulated rupture scenarios that incorporate observed coupling distributions and rheological contrasts.

Historical and potential earthquakes

Historical records include the 1911 events that partially released strain east and west of the gap, while the central locked portion has not produced a documented great earthquake in the instrumental era. Paleotsunami deposits and uplift inferred by researchers at the Smithsonian Institution and UNAM suggest repeat intervals for large ruptures on century to millennial timescales. Scenario analyses by the USGS and Mexican hazard agencies estimate that a full rupture of the Guerrero gap could generate an earthquake in the magnitude 7.8–8.2 range with potential for widespread shaking and tsunami generation affecting Acapulco, Manzanillo, and distant coasts. Interaction with adjacent rupture zones, stress shadow effects from the 1985 Mexico City earthquake, and the timing of SSEs complicate forecast probabilities used by the International Seismological Centre and regional planners.

Mitigation and preparedness strategies

Risk reduction involves integrating scientific monitoring with preparedness led by Protección Civil (Mexico), municipal authorities in Acapulco, and international aid organizations such as the Red Cross. Strategies include updating building codes informed by studies from the Instituto de Ingeniería (UNAM), retrofitting critical infrastructure, tsunami education campaigns coordinated with the Intergovernmental Oceanographic Commission (IOC), and early warning systems developed by the Seismological Service of Mexico and partners like the ShakeAlert project collaborators. Community drills, land-use planning guided by seismic hazard maps from the USGS and UNAM, and cross-border scientific collaborations sustain ongoing efforts to reduce impacts from a potential megathrust earthquake originating in the Guerrero segment.

Category:Seismic gaps Category:Seismology of Mexico Category:Subduction zones