Influence of seismometer misorientation on crustal thickness and Vp/Vs estimated with teleseismic P-wave receiver functions

Abstract

We analyzed the influence of seismometer misorientation on crustal thickness and Vp/Vs estimated with teleseismic P-wave receiver functions simulating orientation errors during the rotation procedure of the horizontal components from true NS-EW (North-South, East-West) to RT (Radial-Tangential) coordinate system. During this procedure, we incrementally added 5° to the azimuth of the NS and EW components. The influence of the misorientation on P-wave teleseismic receiver functions was confirmed by the analysis of different parameters, such as normalized amplitude of P, Ps and multiple phases, reproduction of the radial component and crustal thickness and Vp/Vs estimates. This analysis indicated |45°| as the maximum misorientation allowed to consider crustal thickness, Vp/Vs, and geophysical interpretation reliable. For misorientations larger than |75°|, the reliability is low, and the data could be considered inappropriate for receiver function technique and crustal studies. We also identified some signs of misorientation: P-wave polarity inversion in radial RF trace combined with strong P-wave troughs in the tangential one, low Ps-wave normalized amplitude, reproduction of the radial lower than 90 % for most receiver function traces, and large standard deviations in crustal thickness and Vp/Vs estimates. Since most of the seismometers deployed at Brazilian Seismographic Network were well oriented (only three have orientation errors larger than 45°), in general, previous studies that used data from those stations for estimating crustal thickness and Vp/Vs using the H-k method are reliable. However, in future versions of Brazilian crustal models, the estimates using stations with misorientation larger than |45°| must be recalculated applying an azimuth correction. Finally, since normalized amplitudes are very sensitive to misorientation, the analysis of P and Ps amplitudes in radial receiver functions can be used as a tool to estimate seismometer orientation error and other issues affecting station gain.