УДК 550.348
STUDY OF THE EARTHQUAKE OF THE JANUARY 23, 1880, IN SAN CRISTÓBAL, CUBA AND THE GUANE FAULT
© 2011 Mario Octavio Cotilla Rodríguez and Diego Córdoba Barba
Departamento de Física de la Tierra y Astrofísica I. Facultad de Ciencias Físicas, Universidad Complutense de Madrid. Ciudad
Universitaria, s/n, 28040 Madrid E-mail: macot@fis.ucm.es; dcordoba@fis.ucm.es
All available data on the January 23, 1880, earthquake near San Cristobal, Western Cuba, are compiled and presented here. The earthquake reached a maximum intensity of eight degrees (MSK) and caused three fatalities. It was accompanied by 65 aftershocks and was felt as far away as the Florida Keys. Twentieth century specialists has associated this event, in its day the strongest recorded (Ms = 6.2) in the region, with the Pinar fault. The Pinar fault is well expressed topographically as the boundary between the Guaniguanico Range in the north and an alluvial plain to the south. Most of the major damage caused by the earthquake was located on the alluvial plain, which in consequence has been considered the epicenter area. In the study presented here, the data compiled from the first reports of Father Benito Viñes Martorell, S.J., and Pedro Salteraín y Legarra, indicate that the seismic structure was located in the alluvial plain, and that it was the Guane fault, and not the Pinar fault, that was responsible for the earthquake. The Guane fault, found below the alluvial sediments, extends NE-SW for over 110 km. Its eastern extreme, near San José de las Lajas (La Habana), is linked to another active fault which represents a seismoactive knot responsible for the earthquake of March 9, 1995 (I = 5 degrees, MSK). Seismic events of the Western Cuban region are related to the transpressive interaction of the North American and Caribbean Plates, damped by oceanic structures.
Keywords: Active fault, active tectonics, Cuba, earthquake, San Cristóbal, seismotectonic
1. INTRODUCTION
The presence of a geological fault, for example, a rupture ofearth's crust, is of interest not only from a scientific point ofview, but also from the point ofview ofeconomics and society in general. When these interests converge, specialists typically undertake, among other things, exploration, mining investigations, and research on seismic risk. A prior classification of the faults greatly enables the work of specialists. Two aspects that historically have been taken into consideration are morphology and the expression in the relief. At times, the level of seismic activity of the structures does not permit the recording of both of these aspects. One characteristic observed about the faults is the presence of earthquakes. Thus, it can be possible to link faults well — expressed in the relief with earthquakes that have occurred in a territory, even though their epicenters are relatively far from the faults. Molnar [1988] stated that the systems of faults are the common mechanisms of the accommodation of the motion of the plates in the continental lithosphere. Nur et al. [1993] maintain that quasi — stable areas represent the zones of intersections of faults; in other words, the crust deformations are widely distributed.
During the two last decades (1970—1990), Cuban and European geologists and geophysicists have engaged in an ongoing debate over the existence of the Guane fault (GF) [Cotilla et al., 1991a; Shein et al., 1985a]. Butticaz [1946a] mapped the fault in the southern part of the Pinar
del Río province (Fig. 1). However, more recently, seismologists could not correlate the seismic movements registered along the trace mapped by Butticaz [1946b] as showed Cotillla and Álvarez [2001]. The seismicity of the Western Cuba region is analyzed in this work and in particular that associated with the GF. A determination ofthe existence of the GF is the object of this work. Any such discussion must begin with the work of the two nineteenth century specialists, Father Benito Viñes Martorell, S.J., and Pedro Salteraín y Legarra, who first described the fault and located the strong earthquake of the January 23, 1880, earthquake in San Cristóbal (SC), in Pinar del Río province.
2. GENERAL GEODYNAMICS CONSIDERATIONS
North American plate (NAP) has had a long and complex evolution and at present experiences a differentiated seismic activity. Its largest energetic release is localized along the Pacific Ocean coastline, where the strongest and frequent earthquakes have occurred [Sykes and Seeber, 1985]. There are earthquakes associated to the BartlettCayman (BC) fault at the southern boundary [Mann etal., 1995; Rosencratz and Mann, 1991; Rosencratz et al., 1988]. The eastern boundary is related to the rift zone of the Atlantic Ocean and smaller transforming faults [Sykes and Ewing, 1965]. Opposite to what would be expected, the plate's interior zone suffers strong earth-
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Fig. 1. Scheme of the Pinar del Río province and its surrounding. In it appears: 1) four administrative provinces of the Western Cuba (Pinar del Río, Ciudad de La Habana, La Habana, and Matanzas) with their boundaries; 2) the Guane fault (GF) in discontinue trace; 3) the localities with black squares (1 = Guane, 2 = Pinar del Río, 3 = Viñales, 4 = Consolación del Sur, 5 = Los Palacios, 6 = Bahía Honda, 7 = San Cristóbal, 8 = Isla de la Juventud, 9 = Batabanó, 10 = San José de las Lajas, 11 = Matanzas, 12 = Torriente, 13 = Jagbey Grande).
quakes [Johnston and Kanter, 1990] of magnitudes similar to the ones along the Pacific coast, although they are less frequent; these earthquakes are related to readjustments or reactivation of the crust faults [Johnston, 1989]. The NAP possesses a very diverse mosaic of geological structures: region of very ancient rocks (pre Cambrian) that constitute the basement, and which in consequence are very much strengthened, with a relief that is not very energetic; a younger region of consolidated rocks, surrounding the older one, constituted by the mountainous mass that stand out in the Pacific and Atlantic areas; and a third region that is related with a system of heights and plains articulated in depth and pulled apart in the superficial present — day layout, characterized by large thicknesses of sediments, that widely acts as a transitional zone toward the big morphologic contrasts of the south (Gulfof Mexico and Bahamas Platform) [Johnston and Kanter, 1990]. The Cuban megablock is inserted in this southern border (Cuban microplate), which includes the North Cuban fault, the Eastern Yucatan alignment, and the BC fault system [Ushakov et al., 1979] (Fig. 2). This result is supported by the Bouguer's map of [Prol et al., 1993].
Neotectonics and Geodynamics of Cuba
The Caribbean plate (CP) performs as a discontinuity between the North American and South American plates [Mann and Burke, 1984] (Fig. 2). It experiences a general relative displacement to the east of 2—4 cm/year; in the Cuban sector displacement is 2 cm/year and in Jamaica 1—2 cm/year [DeMets et al., 1990; Deng and Sykes, 1995; Jordan, 1976; Mann and Burke, 1984; Mann et al., 1995; Molnar and Sykes, 1969]. At its western boundary, the Cocos and Nazca plates, belonging to the Pacific plates system, are subducted under the CP. At the eastern boundary, the subduction of the NAP is not so well — defined [Westbrook et al., 1973]. The northern boundary is a system of transforming faults with left — strike displacement and with subduction components to the north of Hispaniola [Mann et al., 1995] and Puerto Rico — Virgin Islands [Mann and Burke, 1984; McCann, 2000; Mc-Cann and Pennington, 1990]. On the northern boundary there is the Mid Cayman rise, 110 km in width [Hol-combe et al., 1973; Rosencratz and Mann, 1991; Ross and Scotese, 1988]. The southern boundary is a complex fault system with left — strike displacement and subduction of the South American and Nazca plates under CP
22°
20°
18°
16°
Gulf of Mexico
ATLANTIC OCEAN
-80°
-70°
Fig. 2. Tectonic scheme of the Caribbean. Heavy black arrows show the sense of the plate movements. With points trace appear the ridges (BR = Beata, NR = Nicaragua). Other structures are: 1) the main faults (BC = Bartlett — Caimán, CNF = Cauto — Nipe, NCF = Nortecubana, OF = Oriente, SEF = Septentrional, SWF = Swan, WPGEF = Walton — Plantain Garden — En-riquillo); 2) passages (MP = Mona, WP = Windward]; 3) islands (Cuba, Hispaniola, Jamaica, Puerto Rico); 4) basins (CB = Colombia, GB = Guatemala, VB = Venezuela); 5) microplates (GM = Gonave, HPRM = Hispaniola — Puerto Rico); 6) troughs (MT = Muertos, OT = Oriente, PRT = Puerto Rico); 7) PBZ = Plates boundary zone.
[Burke et al., 1984; Mann and Burke, 1984; Wooters, 1986].
Cuba is located between the zones of active displacements of the CP and NAP and presents vertical moderated movements that do not exceed 1 cm/year [Alvarez etal., 1990; Hernández, 1987; Hernández et al., 1988]. Díaz et al. [1990] determined the blocks' geometry and disposition for a sector ofWestern Cuba (Cabo de San Antonio — Cochinos), noticing that an increment of the uplifts from west to east, as well as an inclination to north of the entire region. González et al. [2003] consider that these geodetic evaluations are not complete enough to establish the real values of the recent crustal movements of the Cuban structures. These authors argue that the fixed geodetic points not only are insufficient in quantity, but rather have a heterogeneous distribution in addition to a lack of the necessary adjusting control with the net of marigraphs. However, these same authors consider that it is feasible to use them to evaluate tendencies of movements. With considerations in mind, Cotilla et al. [1991a] maintain that Cuba is a megablock ofdifferential ascent in the south of the NAP border that maintains a narrow space and a temporary and energetic relation with the CP through the southeastern zone (Fig. 2).
Various hypotheses attempt to explain the geological develop
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