February 20, 1835 Earthquake: Concepcion, Chile

1835, February 20, (approximately 11:30). There was a destructive earthquake (37N 73W, mag 8.25) and tsunami in the center part of Chile with its source near Concepcion. It is possible that there were foreshock warnings, for on Feb 14, Santiago experienced a weak shock which lasted 20 seconds. The earthquake began in Concepcion with weak tremors which quickly became stronger. For the first half minute no one seemed alarmed but then all the inhabitants fled from their houses. It became impossible, not only to move from one place to another, but even to stand without some kind of support. Even when lying on the ground, one had to hold onto

something in order not to roll about. Some horsemen were thrown from their saddles; others fell, together with their horses, but none of them could remain mounted. There were many instances of seasickness. Then a severe shock which lasted 5-10 seconds, toppled over and destroyed almost all the buildings. In many places cracks opened up in the ground with a deafening crash. A thick cloud of suffocating dust rose into the air from the wrecked buildings and from the ground. All this took about two minutes from the start of the earthquake.The city of Concepcion is situated on a low terrace of the river Bio-Bio on alluvial soils. On the east and north the valley is bounded by hills formed of tertiary shale rock. Apparently, the sedimentary cover settled, owing to the effect of the earthquake. Severe fragmentation occurred at the foot of the hills and the whole valley was dotted with cracks 2-30 cm in width.

Washerwomen repeated, that at the start of the earthquake, the water at the river bank suddenly rose approximately half a metre. A similar occurrence was observed in the mouth of the river at Lirquen.

As a result of the earthquake, more than 50 persons were killed, 10 were seriously injured, 30 were missing and more than 500 suffered concussion or injuries, out of a total population of over 5,000 (700-800, by other accounts). The casualties would have been greater if it had not been summer daytime and the quakes had not increased gradually. There were many cases of persons going out of their mind. Almost all mud brick houses were leveled to the ground. Houses of kiln dried brick suffered less, although they became unfit for habitation; in 2-story houses the upper stories collapsed and the lower were damaged. A single, 2-story building with supporting columns survived - the construction of its roof had just been completed. With the collapse of fireplaces and the falling of thatched roofs, quite a number of fires occurred, but they were all quickly extinguished.

In a technical report, compiled half a year after the earthquake, the percentages of completely collapsed houses, and houses that were damaged but still standing, were estimated as follows according to type: brick, 33 and 67%; mud brick, 71 and 29%; stone construction 95 and 5%.

This quake damaged buildings as far south as Osorno (40.58S, 73.23W), and as far north as San Fernando (34.67S, 71W). The area in which the earthquake was felt, extended from Copiapo (27.33S, 70.38W) in the north, to the island of Chiloe (42.5S, 73.92W) in the south, and from the island of Juan Fernandez (33S, 80W) in the west, where the earthquake was fairly strong, to Mendosa (30.5S,70.92W) in the east.

In Concepcion the ground shook almost continuously for a period of three days. The many aftershocks were preceded by sounds resembling a distant artillery cannonade. More than 300 tremors were counted between February 20 and March 4.

(above from ref #415)

The island of Quiriquina was uplifted 8 feet, Santa Maria Island 8 to 10 feet, Talcahuano 4 to 5 feet, Tubul 6 feet [...] Most of the uplift disappeared during the aftershock sequence. Subsidence was reported in the Maule estuary. (ref #12425)

1835, Feb 20, 15:30 UTC. 36.83 S, 73.03 W, magnitude 8.1 MS, intensity XI, tsunami generated, casualties. (ref #1206)