Abstract
In the light of the November 30th, 2018 (N30) earthquake activity, some neighborhoods of the city of Buenos Aires were shaken by a 3.8 mb earthquake (4.53 km estimated depth). We examined the historical and recent seismic records in order to analyze possible mechanisms related to the distribution of tectonic stresses as responsible for such unusual earthquakes in a region where only very little seismic activity is reported. According to this, at list one historical event occurred on June 5th, 1888 and other small magnitude earthquakes are mentioned since 1848 interpreted as being associated with the Rio de la Plata faulting. But there is, still no consensus about the role of this structure compared to other structures with orientation SW-NE. The lack of evidence to support one over the other structures makes it difficult to analyze these earthquakes. The presence of the Quilmes Trough connecting the Santa Lucía Basin in Uruguay and the Salado Basin in Argentina was recently proposed to play a tectonic role by a system of ENE-WSW trending controlled by extensional faulting related to the beginning of the Gondwana breakup. This depocenter with a thickness of almost 2,000 m of Mesozoic and Tertiary sequences could be acting as a zone of weakness in the crust and therefore responsible for the mentioned earthquake activity. The orientation of this structure correlates well with the present convergence vector between the Nazca and the South American plates and could therefore be propitious for strain release triggering shallow intraplate seismicity. We propose that most of the epicenters from historical and recent earthquakes might be aligned sub-parallel to the principal axis of the Quilmes Trough. Nevertheless, more data is needed to produce a reliable earthquake monitoring system in order to elucidate the tectonic stress regime and the existence of such structures at depth
Highlights
The Rio de la Plata River and the Buenos Aires province in particular, have always been considered to be of low earthquake risk (e.g. INPRES, 2019)
The earthquake recorded near the city of Buenos Aires on November 30th 2018 (N30), reawakened the discussion about the true character of the seismicity in this region as it is located far away from the traditional earthquake prone areas in the north and in the west of the country in Argentina
We present a model with our preferred interpretation suggesting that earthquake activity in this region might be related to the reactivation of the extensional faulting of the Quilmes Trough (QT) mainly because the location of most of the earthquakes is almost parallel to the QT basin axis
Summary
The Rio de la Plata River and the Buenos Aires province in particular, have always been considered to be of low earthquake risk (e.g. INPRES, 2019). The most important historic earthquake in the Rio de la Plata region occurred on June 5th, 1888 at 00:20 local time, with the epicenter located 15 km south of Colonia and 41 km east of Buenos Aires (34o 36’ S, 57o 53’ W) This earthquake was probably the strongest seismic event recorded in the region (Nature, 1884; Navarro, 2012). This earthquake showed that such events could be recorded by the equipment available in a way that allowed identifying the signal and assuring that the phenomena felt by the population was without any doubt an earthquake (Figure 2) This earthquake was strong enough to produce alarm in the towns of Álvarez Jonte, Vieytes and Magdalena (near La Plata, Figure 1) where some residents “heard noises on the roof as if rubble was falling and the wine bottles clinked on the shelves” and it would have had an intensity of four on the Modified Mercalli scale (Jaschek, 1972). This protocol contains some earthquakes in the Buenos Aires province in 1845 and 1967, but they do not appear on any other official reports
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