Publication Date:
2020-02-12
Description:
Typically, when geophysical data sets are gathered, quantities are measured e.g. seismic travel times or amplitudes, which can be modelled to obtain information on the material properties e.g. P- and S-wave velocities and the seismic quality factor, Q. However, in many cases other auxiliary observations are made for which as yet no suitable methods have been derived to obtain information about Earth structure. For example, in northeast Tibet, explosion seismology provides good quality record sections for both P- and S-waves. However, to the south in the northern Lhasa and southern Qiangtang blocks in central Tibet, explosion seismology only provides good quality P-waves. S-waves are not recorded as they are too weak. Here, upper crustal S-waves (e.g. Sg phase) can only be recorded using earthquakes and S-wave reflections from the Moho (SmS phase) can only be recorded using those earthquakes with magnitudes greater than 4.5. Further south in the southern Lhasa block, explosion seismology only provides reasonable quality upper crustal P-waves (e.g. Pg phase) and has difficulty in generating P-wave reflections from the Moho (PmP phase). Yet further south in the Tethyan Himalaya, explosion seismology again provides well recorded PmP waves. Similar patterns of observations can also be recognized in the central Andes of northern Chile and in other regions of young tectonic and/or magmatic activity e.g. Kenya rift, Eifel volcanic region. These observational differences clearly correspond to real differences in some element of crustal structure; most probably variations of Q, heat flow, fluid and/or magma content etc. However, up until now there have been no attempts to actually try and quantitatively model these first-order but nevertheless qualitative observations. This contribution will present examples of the above mentioned observations from the Andes and Tibet and will attempt to discuss possible modelling strategies to quantitatively interpret the above mentioned observations.
Keywords:
550 - Earth sciences
Type:
info:eu-repo/semantics/conferenceObject
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