The 2009 earthquake, magnitude mb 4.8, in the Pantanal Wetlands, west-central Brazil

Abstract

The main goal of this paper is to characterize the Coxim earthquake occurred in June 15th, 2009 in the Pantanal Basin and to discuss the relationship between its faulting mechanism with the Transbrasiliano Lineament. The earthquake had maximum intensity MM V causing damage in farm houses and was felt in several cities located around, including Campo Grande and Goiânia. The event had an mb 4.8 magnitude and depth was 6 km, i.e., it occurred in the upper crust, within the basement and 5 km below the Cenozoic sedimentary cover. The mechanism, a thrust fault mechanism with lateral motion, was obtained by P-wave first-motion polarities and confirmed by regional waveform modelling. The two nodal planes have orientations (strike/dip) of 300°/55° and 180°/55° and the orientation of the P-axis is approximately NE-SW. The results are similar to the Pantanal earthquake of 1964 with mb 5.4 and NE-SW compressional axis. Both events show that Pantanal Basin is a seismically active area, under compressional stress. The focal mechanism of the 1964 and 2009 events have no nodal plane that could be directly associated with the main SW-NE trending Transbrasiliano system indicating that a direct link of the Transbrasiliano with the seismicity in the Pantanal Basin is improbable.

Late Quaternary Cuiabá megafan, Brazilian Pantanal: Channel patterns and paleoenvironmental changes

“…Basin tectonics play an important role in the development of the Pantanal landscape (Soares et al, 1998;Assine and Soares, 2004;Paranhos Filho et al, 2013). Shallow earthquakes commonly registered in the region (Dias et al, 2016) point to differential movements along fault surfaces, and the resulting subsidence of fault blocks controls the generation of accommodation space and the distribution of locations subject to periodic flooding (Assine et al, 2015a). The morphostructural characteristics of the Cuiab a megafan are consistent with a landscape evolving under tectonic control.…”

Probabilistic seismic hazard analysis for a nuclear power plant site in southeast Brazil

“…Acceleration Fourier spectra are inverted to compute source (including moment magnitude), site and propagation term. We also included Mw values from moment-tensor inversions using waveform modelling, such as published by Assumpção and Suárez (1988), Assumpção et al (2011), Agurto et al (2015), Barros et al (2015), and Dias et al (2016). The moment magnitudes computed in these analyses are compared with the regional mR magnitude in Figure 3.The relationship has a gradient of unity and implies that the difference between the two magnitude scales is a constant offset of 0.34.…”

Geology and Geomorphology of the Pantanal Basin

“…An earthquake occurred in 1999, with an epicenter near the apex of the modern depositional lobe of the Taquari megafan, and produced a focal mechanism that indicates an E-W compressive stress [88]. Another recent earthquake occurred in 2009, also situated within the Taquari megafan, revealed an epicenter 6 km deep and focal mechanism indicative of a NE-SW compression [89]. These data are consistent with intra-plate seismicity associated with regional maximum horizontal stress directions in central Brazil, characterized by E-W to SE-NW regional compression [90].…”