EGU21-16259, updated on 04 Mar 2021
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Observation and modelling of the seismc high frequency PKPab precursor at distances larger than 155o

Christoph Sens-Schönfelder1, Klaus Bataille2, and Marcelo Bianchi3
Christoph Sens-Schönfelder et al.
  • 1GeoForschungsZentrum Potsdam, Potsdam, Germany (
  • 2Earth Sciences Department, University of Concepcion, Chile
  • 3Instituto de Astronomia, Geofísica e Ciencias Atmosféricas, Universidade de Sao Paulo, Brazil

Seismic waves traveling through the outer core have been used for a long time to study heterogeneity at the core mantle boundary (CMB) and in lower mantle. Earth's velocity structure opens a window for waves that are scattered at 3D structures in the lower mantle to arrive at the Earth's surface prior to the waves that would propagate in a 1D spherically symmetric model. These precursors are particularly well observed as they are not hidden in the coda waves of earlier phases. At epicentral distances below 140° PKPab and PKPbc waves scattered close to the CMB can arrive as precursors to PKPdf  that travels through the inner core (IC). These waves have been studied extensively and provided important information about the structure of the mantle close to the CMB. However, theory predicts that PKP waves can also be scattered to distances above 155°. These waves have not been well observed before, partly because they arrive at the surface only after the inner core PKPdf phase that has far larger amplitudes at lower frequencies. Here we report on the observation of an emergent arrival of seismic energy at distances above 155° that is consistent with the onset times of scattered PKPbc energy. The key to observe this scattered phase is the use of signals from large deep earthquakes which are strong high frequency sources. As basis for the observation we used records of the Japanese Hi-Net stations that allowed to observe the scattered waves in the distance range between 135and 165o when combining records of two events in Peru and Argentina. The Brazilian seismic network provided observations of a deep Bonin Islands event in the distance range from 145to 175o. Using frequencies around 6Hz we show (A) energy in this frequency band propagates to epicentral distances beyond 170°, (B) attenuation in the IC completely removes the energy of the PKPdf phase, (C) energy scattered close to the CMB arrives prior to PKPab wave forming a precursor that we call PKPab precursor. This observation extends the frequency range and opens a new time-distance window for investigations of deep Earth heterogeneity. 

How to cite: Sens-Schönfelder, C., Bataille, K., and Bianchi, M.: Observation and modelling of the seismc high frequency PKPab precursor at distances larger than 155o, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16259,, 2021.

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