1918 Puerto Rico earthquake

1918 Puerto Rico earthquake
Name	1918 Puerto Rico earthquake
Other names	San Fermín earthquake
Date	1918-10-11
Magnitude	7.1
Depth	15 km
Location	off the west coast of Puerto Rico; near Aguadilla, Mayagüez, and the Mona Passage
Affected	Puerto Rico, United States

1918 Puerto Rico earthquake was a major seismic event that struck off the western coast of Puerto Rico on October 11, 1918, producing strong shaking, a destructive tsunami, and widespread damage across western municipalities. The event occurred in the context of regional tectonics involving the interaction of the North American Plate, the Caribbean Plate, and nearby oceanic features such as the Mona Passage and the Puerto Rico Trench. The earthquake profoundly affected communities including Aguadilla, Mayagüez, Ponce, and San Juan, and influenced later seismic, engineering, and emergency practices in United States territories.

Background and tectonic setting

The western region of Puerto Rico lies near the complex plate boundary between the North American Plate and the Caribbean Plate, where lateral and oblique convergence produces frequent seismicity and occasional large earthquakes. Offshore structures such as the Puerto Rico Trench and the Mona Rift modify strain accumulation and rupture propagation, interacting with submarine faults adjacent to the Mona Passage. Historical seismicity includes events recorded in the 19th century and instruments established by the United States Geological Survey and the Carnegie Institution for Science in the early 20th century. Regional hazards were also shaped by proximity to the Greater Antilles Volcanic Arc and older tectonic features mapped by geologists from institutions such as the Smithsonian Institution.

Earthquake sequence and geology

The mainshock, widely assigned a surface-wave magnitude near 7.1, followed smaller foreshocks and was succeeded by aftershocks that persisted for weeks. Seismograms recorded by stations linked to the International Seismological Summary and by observatories such as the Carnegie Institution Observatory permitted early attempts at epicenter location and focal mechanism analysis. Geological studies after the event described submarine faulting and possible rupture along normal or oblique-slip faults in the Mona Passage region, consistent with extensional stress in portions of the local tectonic regime. Subsequent mapping by researchers associated with the United States Coast and Geodetic Survey and the Puerto Rico Seismic Network helped delineate offshore scarps, submarine landslide deposits, and coastal uplift/subsidence patterns tied to the sequence.

Ground shaking, tsunami, and immediate impacts

Strong ground shaking was reported across western and central Puerto Rico, felt in cities including Aguadilla, Mayagüez, Arecibo, and Ponce, and noticeable in San Juan and on ships in nearby waters. The earthquake generated a tsunami that inundated parts of the western coast and caused damage to ports and coastal infrastructure in harbors such as Aguadilla Harbor and Mayagüez Bay. Eyewitness and contemporary newspaper accounts from outlets like the San Juan Daily described rapid sea withdrawal followed by powerful waves, consistent with submarine displacement or landslide-triggered wave generation. Coastal geomorphology changes were observed by teams from the United States Coast and Geodetic Survey and the United States Army Corps of Engineers, while mariners and fishermen from communities associated with the Puerto Rico Inspection Board noted damage to small craft and piers.

Casualties, damage, and economic effects

The disaster caused numerous fatalities and injuries concentrated in western municipalities; contemporary reports cited dozens to hundreds of deaths and many more injured, though estimates varied among municipal authorities such as the Aguadilla Municipality and the Mayagüez Municipality. Structural damage included collapse or severe impairment of churches, schools, hospitals, and commercial buildings, including edifices tied to institutions like the University of Puerto Rico and facilities near Ponce Harbor. Damage to roads, bridges, and telegraph lines hampered relief and commerce, disrupting trade connections with United States ports and Caribbean neighbors. Economic effects strained local revenues and agricultural production, notably in sugarcane plantations and coffee estates whose operations were linked to businesses in San Juan and trading houses in New York City; insurance and reconstruction financing involved actors such as the First National City Bank and municipal fiscal offices.

Response, recovery, and reconstruction

Immediate response involved municipal officials, medical personnel from hospitals affiliated with the University of Puerto Rico School of Medicine predecessor institutions, and relief supplies coordinated through agencies operating under the United States Department of War and local administrations. Reconstruction efforts combined local labor, contractors from Mayagüez and Aguadilla, and engineering guidance from the United States Army Corps of Engineers, emphasizing rebuilding of critical infrastructure and port facilities. Architectural and building code practices evolved as architects and engineers in Puerto Rican and continental institutions, including the American Society of Civil Engineers, documented failures and recommended stronger masonry anchoring and reinforced concrete use. Philanthropic aid and remittances from diaspora communities in places such as New York City and Philadelphia supplemented governmental relief.

Scientific investigation and legacy

The 1918 event prompted scientific studies by seismologists associated with the Carnegie Institution for Science, the Smithsonian Institution, and the United States Geological Survey, contributing to early understanding of seismic sources in the northeastern Caribbean. Data from the sequence informed later mapping of submarine faults and tsunami generation mechanisms examined by researchers at institutions like the Woods Hole Oceanographic Institution and the Scripps Institution of Oceanography. Long-term legacy includes influence on seismic hazard assessment conducted by the Puerto Rico Seismic Network, improvements in emergency preparedness by municipal governments such as Aguadilla Municipality, and incorporation of earthquake-resistant design principles promoted by the American Society of Civil Engineers and building authorities in San Juan. The 1918 earthquake remains a key historical case for studies linking plate interactions, submarine geology, and coastal impact in the Caribbean basin.

Category:Earthquakes in Puerto Rico Category:1918 natural disasters