Analysis of P-wave travel times for teleseismic earthquakes on nodal seismic surveys
- 1. Velseis Pty Ltd, and University of Queensland, steveh@velseis.com
- 2. University of Queensland, bodee.bignell@uq.net.au
- 3. Velseis Pty Ltd, johnmc@velseis.com
- 4. Velseis Pty Ltd, sstrong@velseis.com
Description
Nodal seismic systems record continuously, and hence record a range of passive events. With severe high-cut filtering it is possible to extract records of teleseismic (distant) earthquakes which are of potential interest in analysis of the crust and upper mantle near the receivers. Cross-correlations of the earthquake P-wave reveal significant inter-nodal time variations, even allowing for near surface static effects. These variations may relate to geology within the sedimentary section, and deeper in the crust. Because of the large channel counts in modern surveys, stacking the teleseismic event can provide significant improvement in signal-to-noise. We have used stacked nodal records to infill between recordings made at permanent seismographs in Queensland. Relative travel-time residuals are of order 1-2s. Teleseisms arriving from different azimuths produce conflicting relative-residual patterns. However, ray-path back projection to upper-mantle depths reveals coherent delay patterns. The observations would be consistent with velocity variations of order 10% occurring in the depth zone 200-400km. This supports lateral variation in the degree of development of an upper-mantle low-velocity zone, with low velocities resulting from increased temperature and partial melting.
Notes
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AEGC_2023_ID249.pdf
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