1918 Puerto Rico earthquake

1918 Puerto Rico earthquake

Mayaguez, Puerto Rico destroyed by the earthquake.] The Puerto Rico earthquake of 1918 was a major earthquake that struck the island of Puerto Rico at 10:14am on October 11, 1918. The magnitude for the earthquake has been reported at around 7.5 (or Level IX in the Rossi-Forel scale used at that time); however, that might not be an exact number. The main-shock epicenter occurred offshore about 10 miles (5 km) from the northwestern coast of the island, somewhere along the Puerto Rico Trench.

The earthquake triggered a tsunami with waves measured at approximately 5.5 meters (20 feet) that lashed the west coast of the island and is remembered as one of the worst natural disasters that have struck the island. The losses resulting from the disaster were approximately 116 casualties and $4 million in property.

Geology of the Earthquake

The epicenter of the 1918 Puerto Rico Earthquake was located in the Mona Passage about 10 miles (5 km) from the northwestern coast of the island, probably along an old fault close to the Puerto Rico Trench. The strongest shakings have been estimated at around 7.3 or 7.5 (Richter scale) or Level IX (Rossi-Forel scale).The resulting tsunami affected primarily the west coast city of Mayaguez and other adjacent towns as well.

Immediate Effects

As a result of the earthquake, numerous structures in the west coast suffered irreparable damages. Factories and production centrals were virtually destroyed, while bridges and roads were severely damaged.

The earthquake caused several mudslides in areas where the magnitude exceeded Level VII, but none of it was deemed as tragic. Also, the river currents were affected, which, in many cases affected the foundations of many bridges which ended up collapsing.

The reported casualties of the earthquake have been estimated somewhere between 91 to 116 deaths. Approximately 40 of these deaths were caused by a tsunami. Also, damages to property were estimated at around $4 million, which was a huge amount at that time.


As a result of the earthquake, a tsunami lashed the west coast of the island, probably 4-7 minutes after the main shock. The highest waves were measured at 5.5 to 6 meters (20 feet) and ended up destroying several coast-side villages. It has been estimated that 40 people were drowned as a direct result of the tsunami.


Several aftershocks were reported immediately after the main earthquake. On October 24 and November 12, two strong aftershocks were reported in the island. However, no damages were reported as a result.

ee also

* Geology of Puerto Rico
* Puerto Rico Trench

External links

* [http://redsismica.uprm.edu/spanish/informacion/terr1918.php Puerto Rico Seismic Network]

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