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krischer / instaseis

Instant high-frequency seismograms from an AxiSEM database
http://instaseis.net
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mu returned by instaseis and location error of receivers #69

Closed lpk-py closed 5 years ago

lpk-py commented 5 years ago

Hi, I got two questions on instaseis and appreciate any clarification .

  1. db.get_seismograms(src, rec, components='Z', ..., return_obspy_stream=False) returns a dict with Z seismogram and another key mu. What is this mu? In the doc, it just says

Return type: A obspy.core.stream.Stream object or a dictionary with NumPy arrays as values

  1. In the direct source-receiver simulations by AxiSEM, the real receiver locations can be different from those requested. For instance, [30.4N, 0E] is requested, but [30.45, 0E] is returned. What makes this shift? AxiSEM provides both coordinates in output files. But Instaseis returns only the requested station locations. So I have no idea about the spatial shift. Is there any way to know this info?
sstaehler commented 5 years ago

  1. The second value is mu (shear modulus) at the source location

  2. In AxiSEM, the receiver is moved to the next GLL point. In Instaseis, the receiver is always at the requested position, since we're doing an interpolation of the wavefield by evaluation of the Legendre polynomials (see the Instaseis paper, section 2.3 https://www.solid-earth.net/6/701/2015/)

lpk-py commented 5 years ago

Thanks for explanation, Simon.