Cariaco: 30 years after Geotectonic context In Venezuela, the contact area of the Caracas earthquake the South American and Caribbean plates runs along the northern bor- der of the country from the state of Faustino Pérez. MAPFRE RE Caracas. Tachira, on the frontier with Colom- Mayte Piserra. MAPFRE RE Madrid bia, to the state of Delta, where the Orinoco flows out, passing through the city of Caracas. This system of area with a radius of 70 km around faults is called Boconó-San Se- the epicenter, and there were 73 bastián-El Pilar, and is where the deaths, 531 injuries and 5,000 more horizontal movement between both In the city of Caracas, about were affected. plates takes place at a rate of be- 400 km far from the epicentre, the Up to 350 aftershocks were tween 2 and 3 cm per year. recorded per day in the weeks fol- tall buildings of Los Palos lowing the main earthquake; these Grandes and Altamira, situated on always had depths lower than 19 km Seismic history very thick sedimentary deposits, and were located along a band 5 km swayed during several seconds. to the South and 20 km to the North The strongest earthquake known The «Ciudad de México» effect was of the El Pilar fault. At the end of Ju- to the area occurred in 1766, and once again felt. ly the number of aftershocks each had a Ms magnitude in the order of day fell to around 50. 7.9, causing damage in Caracas - sit- The earthquake was felt in the uated 300 km from the epicenter - states of Sucre, Anzoátegui, Mona- and was felt as far away as Maracai- gas, Nueva Esparta, Miranda and bo, 800 km away. Other large earth- even in the city of Caracas, about quakes occurred in 1543, 1766, 1794, 400 km far from the epicentre, 1797, 1805, 1839, 1853 and 1929. where the tall buildings of Los Palos It was in 1530 when Cumaná was Grandes and Altamira, situated on shaken by a strong earthquake. But very thick sedimentary deposits, Isoseismal and attenuation map at that time the frail human memo- swayed during several seconds. The ry was not blindly trusted, and the «Ciudad de México» effect was once After the Cariaco earthquake, events were put down in writing, again felt: a amplification of the vi- FUNVISIS* depicted a preliminary thus inaugurating South America’s bration at a large distance from the isoseismal map with information fertile seismic catalogue. Numerous epicenter, in tall buildings situated obtained from 300 intensity ques- seismic movements in the northern where the soft subsoil is very thick. tionnaires which were sent to the af- band of the country have been recorded since that time and, when in 1997, the 30th anniversary of the 1967 Caracas earthquake was being remembered, Cariaco was again to make an appearance in the seismic records. Earthquake details The North-east of Venezuela was shaken by an earthquake with a magnitude of Ms 6.8 at 15: 24 local time (19: 24 GMT) on Wednesday Ju- ly 9, 1997, its hypocenter was at a depth of 10 km, it lasted some 10 seconds and was related to the great El Pilar fault. Its epicenter (10.54 ºN, 63.51 ºW) was placed between Cari- aco and Casanay on the peninsula Miramar building-Cumaná. Headquarters of La Seguridad insurance company. of Araya, some 70 km to the East of The asymmetrical stiffness distribution is showed in the standing shear walls that Cumaná, the capital of the state of surrounded the stairwell and elevator shaft (left side of the building). Sucre. Damage was caused in an Photo: ITSEMAP Venezuela. * This article was written using information obtained from the local press and reports produced by the teams of scientists from FUN- VISIS (Fundación Venezolana de Investigaciones Sismológicas) and ITSEMAP Venezuela, who visited the area of the disaster. 2 Valentín Valiente School, a building of two floors with a symmetrical rectangular shape, faults were de- tected in the design of the structure. Short columns were created when large spaces were opened for win- dows on the ground floor. Also in Cariaco, the Raimundo Martínez school was a four stories building with a reinforced concrete structure that was constructed in 1989. The school was apparently composed of two units with a C plan shape each, and separated by a few centimeters. The ground floor col- lapsed in both buildings. The main causes seem to be the massive pres- ence of short columns together with a lack of lateral reinforcement of the joints of the structure. The collapse of the roof of an open air parking lot used for vehi- cles imported for sale occurred in Preliminary isoseismal map (MMI) of the earthquake of July 9, 1997, Ms=6.8 according Margarita. There was also consider- to FUNVISIS. able damage caused to the undersea cable which supplied electrical en- ergy to Nueva Esparta. fected areas. The area of maximum small family plots, slid rotationally With reference to utilities, the VIII intensity was restricted to an due to liquefaction. surface rupture of the ground and elongated narrow area between With respect to material damage, its posterior movement interrupted Cariaco and Chinguana. In general Cumaná, a city of 350,000 inhabi- the supply of water and electricity to terms, the isoseismals show a clear tants, witnessed the collapse of a many towns in the affected area, es- E-W tendency, in accordance with building, taking with it the life of 21 pecially in Cariaco. the morphology of the valley which people. The Miramar building, cen- The Superintendencia de Se- reveals the presence of the El Pilar trally located on Avenida Perime- guros (the insurance regulator) in fault. A rapid attenuation of the seis- tral, was a 6 stories structure built in Venezuela does not at the present mic energy is also observed, mainly 1979, with large interior openings in time have total figures for the im- in the N-S direction (see map). the first two stories. The building pact of the Cariaco earthquake on was constructed of reinforced con- the local insurance market. Consid- crete with rectangular section ering the low penetration of insur- Effects beams and without transversal rein- ance in the area, it is to be foreseen forcement at the beam-column that the economic impact on the The most surprising effect of the joints of the structure. Only the sec- sector will not be very high. Cariaco earthquake was a surface tion surrounding the stair and ele- rupture of the land of a length of at vator shaft on the first two floors re- Lessons least 30 Km, and an average dis- mained standing; proof of the asym- placement of some 25 cm between metry in the stiffness of the building Local experts have considered Muelle de Cariaco and Las Varas. (see photo). Two floors of the Mira- the Cariaco earthquake to be the There was no visible vertical com- mar building were acquired by the most important seismic event since ponent and the rupture reached up insurance company La Seguridad in the earthquake in Caracas in 1967. to 3 or 4 meters in width. This rup- 1986. In addition to the damage already ture crossed some roads in the area Another three buildings in mentioned, damage was also and made some sections unusable Cumaná suffered serious structural caused to many bahareque homes due to landslides, collapses, and in damage apart from the Miramar (mud and cane), and it will surely be some cases, due to a liquefaction ef- building. The central hospital de a traumatic experience for the fect or loss of strength of water-sat- Cumaná suffered a preventive evac- economy of the area. In addition to urated sediment. The geological ef- uation, but after a professional in- this, the collapse of the recently fects of the earthquake were howev- spection, it was revealed that only constructed office buildings and er concentrated along the coast and received slight non-structural dam- schools deserves a more careful in sparse locations in the interior. age. analysis. A warning lesson for a Liquefaction, collapses and land- In Cariaco, at less than 10 km country in which large earthquakes slides occurred mainly on re- from the epicenter, and only a few have occurred every 30 years on av- claimed land, river or channel hundred meters from the rupture of erage during this century. Too short banks and the coast. Some small the surface, two schools collapsed, a time to forget, but long enough to earth dams used in the irrigation of burying 30 schoolchildren. In the prevent. 3.