DETERMINACIÓN DE VELOCIDADES P Y S DE LAS UNIDADES ROCOSAS AFLORANTES EN EL ÁREA METROPOLITANA DE MÉRIDA, VENEZUELA
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Universidad Industrial de Santander
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Para los alrededores del área metropolitana de Mérida se determinó, mediante sísmica de refracción, las velocidades de propagación de las ondas P (Vp) y S (Vs) en los afloramientos de los distintos tipos de rocas predominantes de las asociaciones Sierra Nevada, Tostos y Mucuchachí, y las formaciones Palmarito, Sabaneta, La Quinta, Aguardiente, La Luna y San Javier. Para los casos de las asociaciones Sierra Nevada y Tostos, la Vs se calculó a partir de la Vp y el coeficiente de Poisson. La extensión de las líneas sísmicas varió de 24 m a 26 m, utilizando en todos los casos 48 geófonos verticales e igual número de horizontales, y como fuente de energía una mandarria. La adquisición de los registros sísmicos fue llevada a cabo directamente sobre los afloramientos, por lo que en los casos de rocas más competentes no se pudo insertar directamente los geófonos, y como medida alternativa se utilizó la técnica de insertarlos en bloques de concreto. Los arribos de las ondas P se obtuvieron de los registros de los geófonos verticales y los de la S (SH) de los horizontales. Los resultados de este trabajo ofrecen, información de las velocidades de las ondas P y S de las principales tipo de roca en superficie, y puede servir de complemento a investigaciones de sísmica profunda.
For the predominant rock type of outcrops in the surroundings of the metropolitan area of Mérida city,compressional (Vp) and shear (Vs) wave velocities were determined using seismic refraction. These outcrops correspond to the Sierra Nevada, Tostos, and Mucuchachí Associations, and Palmarito, Sabaneta, La Quinta, Aguardiente, La Luna, and San Javier formations. Vs values for Sierra Nevada and Tostos Associations were estimated from Vp values and laboratory measured Poisson ratio. The length of the seismic lines ranged from 24 m to 26 m, using for all cases 48 vertical geophones and an equal number of horizontal geophones. A sledgehammer was used as energy source. The seismic acquisition was carried out directly from the outcrops. However, for the cases of more competent rocks, the geophones could not be placed directly, so they were inserted in concrete blocks to keep them firm and vertical. The P waves arrivals were obtained via the vertical geophones and the S (SH) waves arrivals were obtained via the horizontal geophones. The results of this investigation offer information of P and S wave velocities of the main surface rock types, which could be useful as complementary data for future deep seismic sounding studies.
For the predominant rock type of outcrops in the surroundings of the metropolitan area of Mérida city,compressional (Vp) and shear (Vs) wave velocities were determined using seismic refraction. These outcrops correspond to the Sierra Nevada, Tostos, and Mucuchachí Associations, and Palmarito, Sabaneta, La Quinta, Aguardiente, La Luna, and San Javier formations. Vs values for Sierra Nevada and Tostos Associations were estimated from Vp values and laboratory measured Poisson ratio. The length of the seismic lines ranged from 24 m to 26 m, using for all cases 48 vertical geophones and an equal number of horizontal geophones. A sledgehammer was used as energy source. The seismic acquisition was carried out directly from the outcrops. However, for the cases of more competent rocks, the geophones could not be placed directly, so they were inserted in concrete blocks to keep them firm and vertical. The P waves arrivals were obtained via the vertical geophones and the S (SH) waves arrivals were obtained via the horizontal geophones. The results of this investigation offer information of P and S wave velocities of the main surface rock types, which could be useful as complementary data for future deep seismic sounding studies.
Keywords
Seismic refraction, compressional wave, shear wave, rocky outcrops, metropolitan area of Mérida, Sísmica de refracción, ondas P y S, afloramientos rocosos, zona metropolitana de Mérida