Earthquakes of Peru
South America's west coast is a segment of the circum-Pacific seismic belt, where more than two-thirds of the world's large-magnitude earthquakes occur. The rugged Andes and offshore Peru-Chile trench have been the breeding ground for devastating earth disturbances for centuries past. The evidence, earthquakes in Colombia-Venezuela, 1875, claimed 16,000 victims; Ecuador, 1797, 41,000; Peru, 1746, 5,000; and Chile, 1939, 30,000.
In the Callejón de Huylas, the survivors near Ranrahirca cross the mud and debris which buried their homes after the May 31 earthquake.
Peru's earthquake annals date back over 400 years, to 1553, but the first descriptive account of a strong shock tells of a terremoto that killed 30 people and destroyed much of Arequipa in 1582.
The most deadly earthquake in Peru's history before 1970 struck Lima in October 1746. At least 5,000 persons were killed, many of them when a seismic seawave (tsunami) swept the coast. Because of the Lima earthquake, there is an annual festical of the Miracle Christ in Peru, and to this day, the custom of wearing purple during the month of October is observed in commemoration of that event.
The tops of four 50-foot palm trees are all that remain of the city square in Yungay, Peru, buried to an average depth of ten feet by an earthquake triggered icefall and mudslide.
The slide of ice, mud, boulders, and debris took about five minutes to bury Ranrahirca, destroying the town for the second time in its history
During the next 200 years, the most destructive shocks in Peru centered in and south of the Callao-Lima area, causing much damage in Camaná, Callao, Abancay, and Yanaoca.
Then, on November 10, 1946, a magnitude 7.3 earthquake, centered in the region of the May 1970 shock, generated landslides that annihilated the town of Quiches (northeast of Chimbote), and badly damaged Conchucos and Mayas. An estimated 1,400 deaths resulted. This shock in Ancash Department was marked by a new break in the Quiches Fault which cuts across the Peruvian highlands among the Andes. A Peruvian scientist and his assistants traveled 25 days on horses and mules to inspect the remote epicentral region of the tremor. They found a pair of scarps 2 miles apart, with the land between sunken 10 feet.
A moderate earthquake located directly under a city can create a situation far out of proportion to its scientific significance. It happened in May 1950 in the old Inca city of Cusco (in southern Peru) which sustained severe damage, while few other towns felt anything.
An interesting result was the destruction of buildings constructed in recent centuries since the Spanish conquest, while the stone walls and doorways constructed by Incaic artisans were nearly all intact, showing little or no effects of the earthquake. Since the Incas were not known to use mortar between stones in construction, this is even more remarkable. They skillfully fitted together great massive stone blocks in an extremely strong, interlocking manner. The extreme damage in Cusco (about 63 percent of the buildings had to be reconstructed) was due to poor construction of adobe dwellings, and to the thickness of alluvial gravels and degree of soil saturation.
One of the strongest shocks, in October 1966, also centered near the 1970 epicenter. Several inhabitants of the Huacho area were killed, and over 20,000 were homeless in Huacho, the most severely damaged village. At the time of this shock a religious festival (perhaps associated with that mentioned earlier, established in commemoration of the great Lima catastrophe in October 1746) was being held in Callao; several died when some churches collapsed. Landslides and huge ground cracks were noted along the Pan American Highway, and over 2,000 houses sustained severe structural damage in Lima.
Landslides, ground fractures, and overturned trees also accompanied a magnitude 6.9 tremor in northern Peru in June 1968. Forty-six persons were killed in Moyobamba.
A moderate-magnitude earthquake, only slightly larger than that which devastated Cusco in 1950, swept through the Pariahuanca area of central Peru in October 1969. Comas village was 60 percent destroyed, and Lampa and Chilifruta were completely razed. Many landslides resulted from this tremor which caused 136 fatalities.
In May 1960, southern Chile was struck by a series of earthquakes that rank with the greatest of historical record. The sequence of destructive shocks occurred along 500 miles of the coastal area south of Concepción. In comparison, the May 31, 1970, Peru earthquake and aftershocks seem less powerful; however, the death toll resulting from mammoth landslides, and flooding due to burst dams have placed this earthquake among the most devastating ever in the Americas.
Abridged from Earthquake Information Bulletin, September - October 1970, Volume 2, Number 5.