Estimating seismometer component orientation of the Brazilian seismographic network using teleseismic P-wave particle motion analysis and directional statistics

Abstract

Seismometer component orientation is one of the most critical parameters for seismology, especially for methods that take wave field polarization effects into account, such as receiver functions, seismic anisotropy, surface wave dispersion and seismic tomography. Using P-wave particle motion combined with directional statistics, we estimated the orientation for 90 stations of the Brazilian Seismographic Network (RSBR), corresponding to 105 seismometers. The difference between the number of stations (90) and seismometers (105) is due to instrument replacement during station operation. We observed that 81 seismometers have an orientation of ±5° and 19 seismometers greater than ±5°. Only one seismometer has an orientation greater than 90° (BOAV station). ON and BR are the subnetworks of RSBR with the largest number of seismometers with orientation errors bigger than ±10° (6 for each one) and NB is the only subnetwork with no misoriented station. All the estimated orientations were close to the measured in the field, which is evidence that our approach is more accurate to detect misoriented stations than previous studies that analyzed the orientation of RSBR stations. The Watson's U2 statistical test indicated that the back azimuth deviations for Precambrian Basement and Phanerozoic Cover were significantly different, suggesting that the regional geology could affect back azimuth estimates.