科研之友
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摘要
The strong sensitivity of seismic surface waves to the Moho is evident from a mere visual inspection of their dispersion curves or waveforms. Rayleigh and Love waves have been used to study the Earth%26apos;s crust since the early days of modern seismology. Yet, strong trade-offs between the Moho depth and crustal and mantle structure in surface-wave inversions prompted doubts regarding their capacity to resolve the Moho. Here, we review surface-wave studies of the Moho, with a focus on early work, and then use model-space mapping to establish the waves%26apos; sensitivity to the Moho depth and the resolution of their inversion for it. If seismic wavespeeds within the crust and upper mantle are known, then Moho-depth variations of a few kilometres produce large (%26gt;1%) perturbations in phase velocities. However, in inversions of surface-wave data with no a priori information (wavespeeds not known), strong Moho-depth/shear-speed trade-offs will mask similar to 90% of the Moho-depth signal, with remaining phase-velocity perturbations similar to 0.1% only. In order to resolve the Moho with surface waves alone, errors in the data must thus be small (up to similar to 0.2% for resolving continental Moho). With larger errors, Mohodepth resolution is not warranted and depends on error distribution with period. An effective strategy for the inversion of surface-wave data alone for the Moho depth is to, first, constrain the crustal and upper-mantle structure by inversion in a broad period range and then determine the Moho depth in inversion in a narrow period range most sensitive to it, with the first-step results used as reference. Prior information on crustal and mantle structure reduces the trade-offs and thus enables resolving the Moho depth with noisier data; such information should be used whenever available. Joint analysis or inversion of surface-wave and other data (receiver functions, topography, gravity) can reduce uncertainties further and facilitate Moho mapping.
- 出版日期2013-12-8
