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Abstract: Analysis of teleseismic records obtained in two broadband seismic stations of three components located on the Andean region of Colombia is presented in this work. The two stations are located at the Western Cordillera (WC), station BOL, and at the Central Cordillera (CC), station PBLA. The analysis of seismograms was performed by inversion of the receiver functions (RF) in order to obtain the crustal velocity structure beneath the receivers. The receiver function is a spectral ratio obtained from teleseismic earthquakes recorded by broadband seismic stations, which allows the calculation of the velocity structure beneath the receiver by removing source effects in the horizontal components of the seismic traces. Data stacking was performed in order to improve signal to noise ratio and then the data was inverted by using two optimization algorithms: a genetic algorithm (GA), and a simulated annealing algorithm (SA). The present work calculates the receiver functions using teleseismic earthquakes at epicentral distances (Δ) ranging between 30° and 90° and recorded at the two stations within the years 2007 and 2009. Delay times between P and PS waves converted at the Moho boundary were used to constrain the velocity structure. The receiver functions at the stations were generated from seismic events within a broad range of back azimuth. Data from gravity and magnetism were also used during the geophysical survey. The depth of the Moho boundary was found to be at 40 km in the WC beneath station BOL and at 43 km in the CC beneath station PBLA. The upper crust, with a thickness of 5 km, is characterized by a shear wave velocity of about 3.0 km s−1; the shallower layers, at approximately 1.0 km, have shear wave velocities between 2.2 and 2.6 km s−1, which corresponds to sediments overlying the upper crust. These observations support the hypothesis of a thickness of the crust at the root of the mountain range to be between 32 and 50 km. The calculated receiver functions were compared with artificial ones generated from the inversion of 48000 models of horizontal layers for each station using a GA and an SA that allowed a satisfactory coverage of all the sample space in order to avoid non-unique solutions. Beneath station BOL a moderate low-velocity zone (LVZ) was found, which was caused by accretionary processes of the ophiolite complex in the WC. [Copyright &y& Elsevier]

Triaxial acelerografic data related to replies of Armenia earthquake in Colombia (25-01-99, Mw=6.2) have been used to determine the transfer function of Soft Formation / Hard Rock in two sites of Armenia city by using a neuronal network. This network was trained with spectral data of HARD ROCK as input parameter and spectral data of Soft Formation as output parameter for N-S and Z components. The error of the neuronal network respect to the training data was of 0,01%. It allowed to simulate spectral data for the E-W component of registries with a quadratic mean error minor to 8%. It was possible to observe that with these few records used, the neuronal networks facilitate the process of deduction of transference functions linear and not-linear oriented to the dynamic ground evaluation. [ABSTRACT FROM AUTHOR]

Abstract: The Abanico del Quindío (AQ) fan, a volcaniclastic deposit from the Ruiz–Tolima volcanic complex (RTVC), Colombia, provides insight into recent deformation in the Central Andes. The use of geological observations, geophysical measurements, and estimates of fault-scarp ages constrain timing of recent tectonic activity. Gravity and magnetic analyses, along with geomorphologic cartography, allow the detection of lateral variations in basement distribution and at least three structural trends that cut the AQ: the Armenia fault (NNE), El Danubio fault (NNW), and Hojas Anchas fault (E–W). Recent deformation in the zone results from slip on the Armenia and El Danubio faults and suggests a maximum interval magnitude of 5.1< M w <6.3, with ages ranging between 2560±480yr B.P. and 4120±780yr B.P. Although no surface ruptures are associated with historical events on the fault segments in this zone, blind structures may have influenced the hypocentral distribution of events recorded after the Armenia Earthquake (M w 6.2, 25-01-1999). Further geophysical studies are needed to understand the Romeral Fault System and assess the earthquake hazard for the city of Armenia. [Copyright &y& Elsevier]

A letter to the editor is presented about the lithospheric structure of the Latin American and Caribbean territory.