Determination of accurate earthquake locations to study earthquake fault geometry

• Grant number: 14/09915-4
• Support Opportunities: Scholarships abroad - Research Internship - Scientific Initiation
• Start date: August 15, 2014
• End date: December 14, 2014
• Field of knowledge: Physical Sciences and Mathematics - Geosciences - Geophysics
• Principal Investigator: Marcelo Sousa de Assumpção
• Grantee: Caio Henrique Ciardelli
• Supervisor: Andreas Rietbrock
• Host Institution: Instituto de Astronomia, Geofísica e Ciências Atmosféricas (IAG). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Institution abroad: University of Liverpool, England
• Associated to the scholarship: 13/24001-6 - Study of the Montes Claros Seismogenic Fault with Correlations of P- and S-wave Phases., BP.IC

Abstract

During his internship, the student will work with two earthquake sequences. The first one occurred in a small city called Montes Claros, located in northern Minas Gerais state. Altogether, seven events with magnitude in a range of 3-4 mb have occurred in 2012-2014 period. These earthquakes were big enough to be detected at distances up to ~1000 Km, what make possible to use the Brazilian Regional Seismic Network to locate them. The second sequence occurred in Iquique, northern Chile. It started with a magnitude 6.6 earthquake, in mid-March, and proceed with a lot of aftershocks. The huge 8.2 magnitude earthquake, occurred in April 1, is also included. All the events with magnitude down to 4.0 mb were also recorded by many stations of the Brazilian Network. The project objective is to use the Regional Network to locate both the Iquique as the Montes Claros events. In order to achieve better results, the student will use a 3-component cross-correlation program, developed own his own using Python language and the ObsPy (Beyreuther et al., 2010), Matplotlib (Hunter, 2007) e NumPy (Jones et al, 2001) packages, during his undergraduate research project, funded by FAPESP. The algorithm can perform the cross-correlation using the standard technique, which consists in use a single event as reference to correct all the others. Nevertheless, it doesn't lead to good results every time because, seldom, all events have a similar waveform with the reference. Trying to minimize this problem, he developed a new technique. This other algorithm starts searching for the most similar event with the reference and, then, correct him. The idea is that, once an event has already been corrected, it also can be used as reference to correct others. So, the next event that will be correlated will be the most similar with the initial reference or with any event already corrected. This process continues until all events have been correlated. This technique was called "branched correlation" and has already been applied with good results to a 2012-2013 events sequence, recorded by a local network located in Montes Claros, and used in the first study of the Montes Claros sequence (Hans et al., 2014). The double-difference time earthquake location algorithm, implemented in the HypoDD code (Waldhauser et al., 2000), will also be used to re-locate the events, improving its relatives locations and better defining the seismogenic fault plane. His supervisor in Liverpool (Andreas Rietbrock) has a long experience in studies of South American earthquakes (especially in Chile) and is taking part of the team of a recently submitted FAPESP thematic project. Caio's internship in Liverpool is the first of many other cooperations planned for the next few years. (AU)