The 12 Dic, 1953, Earthquake, Ms 7.3, Ecuador-Peru border region: A Case Study for Applying the New INQUA Intensity Scale
by
Kervin Chunga
Dipartimento di Scienze Chimiche e Ambientali, Università dell'Insubria, Via Vallegio 11, 22100, Como, Italia
Coauthors: Yolanda Zamudio, Gloria Marín (Instituto Geofísico del Perú), José Egred (Instituto Geofísico del Ecuador), María Quiñónez, Diego Iturralde (ESCIGEA, Universidad de Guayaquil, Ecuador)

The INQUA Scale is a newly proposed Macroseismic Intensity Scale, based solely on Earthquake Environmental Effects (EEE). This Scale has been discussed during the two Local Meetings carried out in Guayaquil, Ecuador. One of the points raised throughout the Meetings, was the importance of post-earthquake damage assessment. Moreover, we briefly reviewed the modern antiseismic building codes, in order to reconsider data relative to damage on buildings and make them confrontable with those of historical earthquakes. It's obvious, in fact that ancient buildings were constructed with different engineering standard from present ones. Regarding the INQUA Scale, the participants, technical and scientific community, has considered this new Scale as an excellent tool for the environmental analysis of past and contemporaneous Ecuadors earthquakes.

Indeed, the closeness of the Ecuador to the Subduction Zone (where the Nazca Plate subducts beneath the South American Plate) and the significant active and capable seismogenetic structures that affect the continental block, make it highly susceptible to tectonic and tsunamigenic events. Historically, from 1557 to 2000, 122 seismic events have been reported in Ecuador (in the range of MM Intensity VIXI). The following earthquakes generated important tsunamis along the Ecuador's coastal range: (A) The 31st Dec 1906, earthquake, Ms 8.8, located about 138 Km W from Tortuga, Prov. Esmeraldas. This earthquake is classified as the sixth largest earthquake worldwide in the past 100 years. (B) The 2nd Oct 1933, earthquake, Ms 6.9, located offshore from Peninsula Sta. Elena. (C) The 12th Dec 1953, earthquake, Ms 7.3, located up to 23 Km NW from Tumbes, Peru-Ecuador border region. (D) The 19th January 1958, earthquake, Ms 7.8, Ecuador-Colombia boundary. (E) The 12th Dec 1979, earthquake, Ms 7.9, located offshore from San Lorenzo, Ecuador-Colombia boundary. (Espinoza, 1992; Chunga et al., 2002).

Information about several earthquakes was recompiled in order to apply the INQUA Scale. In particular, we have selected the 12th Dec 1953, earthquake (Ms 7.3) as a sample event, because of two reasons: (a), the necessity to improve the information available for this event in Ecuador, and (b) the bibliographic documentations retrieved, that provide us an excellent description of the ground environmental effects in several cities close to the epicentral area (i.e., Silgado, 1957; www.vivatumbes.com/tumbes_1925/Terremoto.htm). The 1953 earthquake, struck the South Ecuador-Northwest Peru border region at 12.31 am local time, with 7.3 Ms magnitude and VII-VIII Intensity (MM-1931 Scale) (Silgado, 1953). Its epicenter was located offshore 23 Km NW from Tumbes and 155 Km SW from Guayaquil. The maximum intensities was felt in Tumbes-Corrales-Celica, respectively.

In the Tumbes and Corrales populations (Perú), 6 dead and at least 20 injuries were reported. Many local witnesses perceived a time shaking of about 40 seconds. Numerous material damages to both, Peruvian (San Juan, Zorritos, Santa Cruz, El Alto y Talara) and Ecuadorian (Gonzamaná, Celica, Azogues, Malacatos) villages occurred. Minor damage was reported in the Guayaquil city. Still, the tectonic source of this event has not been well-defined. According to our preliminary surveys, it seem possible to suggest a linking with either active faults (Jubones-Tumbes or Amistad) close to the epicentral area, associated to the compressive geodynamic model of the Subduction Zone. The Isoseismals of this earthquake were elongated about NW-SE (see Intensity Map of Silgado, 1957), almost parallel to the trend of the Jubones-Tumbes fault. For its closeness to this seismogenetic structure, and for its similar structural trend, the 1953 earthquake, could have direct relationship with the fault previously mentioned.

The documentation retrieved (Silgado, 1957) gave us an well description on the ground environmental effects accompanying the 1953 earthquake. The most significant effects occurred at the following sites: (1) large and deep cracks affecting alluvial soil with NW-SE trending reached up to 40 cm wide at Tumbes, on the Panamericana road, and up to 1.5 m wide between Zorritos and Tumbes; (2) significant liquefactions in alluvial sediments were observed in the Puerto Pizarro estuaries and other localities; (3) dry springs were activated in the Quebrada Bocapan; (4) significant earthquake fountains, 60 cm high, and sandy ground cracks with E-W trending were generated in the Puerto Pizarro seashore; (5) small landslides affecting loose sediments were frequent in the epicentral area, among them: El Alto, the surrounding of Zorritos, and many other villages along the Tumbes River canyon and flat settings. Small tsunamis with run-up heights of 20 cm were reported in La Libertad, northern coastal of the Peninsula St. Elena (Ecuador), about 138 Km NW from epicenter (Espinoza, 1992). Based on these field reconnaissance, carried out by Silgado (1957), and on our preliminary assessment, INQUA Intensity of IX should be well assigned to Tumbes and one INQUA Intensity VIII to the Corrales (Perú) and Celica (Ecuador) settings.

References

Chunga K., Dumont J.F. 2002. Susceptibilidad tsunamigénica en las zonas costeras del Golfo de Guayaquil y correlación sedimentológica de un depósito de tsunami en el área de Villamil Playas. Mem. VIII Congreso Ecuatoriano en Ciencias de la Tierra. Guayaquil, 17 páginas.

Espinoza J., 1992. Terremotos tsunamigénicos en el Ecuador. Acta Oceanográfica del Pacífico, 7(1), 21-28.

Michetti, A.M.; Esposito, E.; Gürpinar, A.; Mohammadioun, B.; Mohammadioun, J.; Porfido, E.; Rogozhin, E.; Serva, L.; Tatevossian, R., Vittori, E., Audemard, F., Comerci, V., Marco, S. McCalpin, J., Mörner, N.A. (2004). The Scale INQUA: An innovative approach for assessing earthquake intensities based on seismically-induced ground effects in natural environment. Special paper. Memorie - Descrittive della Carta Geologica d'Italia, Vol. LXVII, E. Vittori and V. Comerci eds.. APAT-Dip. Difesa del Suolo/ Servizio Geologico d'Italia. Roma.

Silgado, F.E. (1957). El movimiento sísmico del 12 de diciembre de 1953. Boletín de la Sociedad Geológica del Perú, vol.32, Part 2, pp.225-238.

Date received: July 22, 2005

Copyright © 2005 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # caqy-56.