Estudo da atividade sísmica em São Caetano - PE em 2007

Abstract

In this campaign up to nine three-component digital seismographic stations were deployed and the collected data was used to determine hypocenters and focal mechanism. A total of 214 earthquakes, recorded at least by three stations, were analyzed. To determine hypocenters and time origin the HYPO71 program was used assuming a half-space model with parameters: V P (P-wave velocity) equal to 5.90 km/s and the ratio V P /V S 1.70, where V S is the S-wave velocity. The earthquakes hypocentral distribution was approximately 4 km long and agrees with the NE-SW direction of the Pernambuco Lineamento branch. Hypocenters depth range from 2 to 8 km. The composed focal mechanism was made from a group of 14 selected earthquakes. We try firstly to find the fault plane solution matching the polarity distribution at stations, using the FPFIT program. The result was 43 deg ± 15 deg for strike, 59 deg ± 9 deg for dip and -142 deg ± 15 deg for rake. We also fitted a plane using the hypocentral distribution to obtain the dip and azimuth of the hypocentral distribution. The results obtained by this fit were 58 deg for the azimuth, 55 deg for the dip and -155 deg for rake. This result shows a mechanism of a strike-slip dextral fault with a normal component. This dissertation shows, once more, that there is a good correlation between the seismic activity and geological features in the region near the Pernambuco Lineament and its NE branches.144

Intraplate earthquake swarm in Belo Jardim, NE Brazil: reactivation of a major Neoproterozoic shear zone (Pernambuco Lineament)

“…The swarms of Caruaru (Ferreira et al 2008), Belo Jardim and São Caetano (Lima Neto et al 2009) all have hypocentral depths in the range 3–6 km. Although the maximum magnitude known to have occurred so far near the Pernambuco Lineament was 4.0 m R , the lineament is probably a weak zone and a seismic rupture with lateral extent of a few tens of kilometres cannot be completely ruled out.…”

“…2a). The recent activity (2006/2007) in São Caetano, with magnitudes up to 4 m R , was shown by Lima Neto et al (2009) to have occurred on a single SW–NE trending strike‐slip fault, similar to the 2002 Caruaru sequence (Ferreira et al 2008). Interestingly, these two strike‐slip sequences occurred on SW–NE trending lineaments which branch off to the north from the major E–W structure of the Pernambuco Lineament, as seen in Figs 1(b) and 2(a).…”

“…The grey circle and focal mechanism (1) are the Belo Jardim sequence studied in this paper. The other three focal mechanisms are: 2 = São Caetano 2007 (Lima Neto et al 2009), 3 = Caruaru 1991 (Ferreira et al 1998) and 4 = Caruaru 2002 (Ferreira et al 2008). The open triangle denotes the regional station CAUB near Caruaru.…”

Estudo da sismicidade ao sul do Lineamento Pernambuco em 2010

“…Os hipocentros foram determinados com o programa HYPO71 (Lee & Lahr, 1975) que tem sido utilizado com sucesso no estudo da sismicidade no Nordeste do Brasil (Ferreira et al, 1987(Ferreira et al, , 1995(Ferreira et al, , 1998(Ferreira et al, e 2008do Nascimento, 1997;Lima Neto et al 2009). A relocação dos hipocentros foi realizada com o algoritmo da dupla diferença HypoDD (Waldhauser, 2001).…”

“…Nesta região, diversos eventos sísmicos vêm sendo relatados desde o século XIX e, nos últimos anos, tem se manifestado de forma mais intensa e numerosa (Ferreira et al, 2008;Lima Neto et al, 2009;Lopes et al, 2010). Além disso, esta região possui importantes estruturas tectônicas mapeadas, destacando-se o Lineamento Pernambuco, uma zona de cisalhamento de escala continental com 700 km de comprimento que aparece claramente na superfície (Davison, et al, 1995).…”