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1918 San Fermín earthquake facts for kids

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1918 San Fermín earthquake
UTC time 1918-10-11 14:14:42
ISC event 913306
Local date October 11, 1918 (1918-10-11)
Local time 10:14:42
Magnitude 7.1 Mw
Depth 15 km (9.3 mi)
Epicenter 18°48′N 67°13′W / 18.8°N 67.22°W / 18.8; -67.22
Type Unknown
Areas affected Puerto Rico
Total damage $4–29 million USD
Max. intensity IX (Violent)
Tsunami Yes
Casualties 76–118

The 1918 San Fermín earthquake, also known as the Puerto Rico earthquake of 1918, struck the island of Puerto Rico at 10:14:42 local time on October 11. The earthquake measured 7.1 on the moment magnitude scale and IX (Violent) on the Mercalli intensity scale. The mainshock epicenter occurred off the northwestern coast of the island, somewhere along the Puerto Rico Trench.

The earthquake triggered a tsunami with waves measured that swept the west coast of the island. The combined effects of the earthquake and tsunami made it one of the worst natural disasters that have struck the island. The losses resulting from the disaster were approximately 76–118 casualties and $4–29 million in property damage.


The epicenter of the 1918 San Fermín earthquake was located in the Mona Passage off the northwestern coast of the island. The strongest ground shaking has been estimated at intensity IX on the Mercalli intensity scale. The resulting tsunami affected primarily the west coast towns of the island (primarily Mayaguez).


Terremoto Mayaguez 1918
Damage caused to the "La Habanera de Infanzón y Rodríguez" building in Mayagüez

Numerous structures in the west coast suffered irreparable damage. Factories and production facilities were virtually destroyed, while bridges and roads were severely damaged. The earthquake caused several mudslides in areas where the intensity exceeded Level VII, but none caused numerous deaths. Also, the river currents were affected, which, in many cases affected the foundations of many bridges, resulting in their collapse. Telegraph cables under the ocean were damaged, cutting off the island from outside communication for a time.

Simulation of the results of the tsunami on the coast of Aguadilla, Puerto Rico

The reported casualties of the earthquake have been estimated somewhere between 76 and 116 deaths. Approximately 40 of these deaths were caused by the tsunami which swept shore communities. Damage to property was estimated to be between $4 and 29 million.

In Mayagüez, the largest city affected, 700 masonry buildings were damaged and 1,000 wooden houses, so many people were homeless. Major buildings like the church, post office and hall were severely damaged. With fear because of the aftershocks, many people camped out in the hills for weeks.


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 estimated at 6.0 m (19.7 ft) in Point Agujereada, 4.5 m (15 ft) at Point Borinquen, and 5.2 m (17 ft) at Point Jiguero. Several coastal villages were destroyed and it has been estimated that 40 people drowned (32 in Aguadilla alone) 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 on the island. However, no damage was reported as a result.


See also

Kids robot.svg In Spanish: Terremoto de san Fermín de 1918 para niños

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