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Receiver function
A receiver function technique is a way to model the boundary layers and structure of the Earth by using the information from teleseismic earthquakes recorded at a three component seismograph.
A teleseismic P-wave will generate P to S conversions at boundaries, such as the Moho (crust-mantle boundary), beneath the seismograph. The difference in travel time between the generated S-wave and P-wave contains information about the distance to the boundary and if further reverberations are included more detailed structure can be resolved. This is done by deconvolution of the incoming vertical and longitudinal components of the seismogram which removes the common part of the components - namely, the source and travel path information. The resulting waveform is the receiver function.
Similarly, a teleseismic S-wave will generate an S to P conversion beneath the seismic station.
Method
The primary method for creating a receiver function is based on analyzing the product of waves that pass from the mantle through the Moho boundary. This is because there are large compositional differences between the crust and the mantle, thus causing large differences in seismic waves as they pass through the discontinuity.[1] Since receiver functions depend on wave refraction and reflection from P waves in the mantle, they can only be generated properly if the seismic event occurs between 30 and 80 degrees below the horizon of the seismograph station. The method is also most effective when the seismic event causing the waves occurs more than 600km below the surface, which is important to avoid surface interference.[2]
As a P wave in the mantle pass upwards through the Moho, it is largely converted into an S wave. This S wave is picked up by the seismometer on the Earth's surface via vertical motion, and alone can be used to analyze discontinuities within the Earth. In addition to these S waves, the P wave traveling through the Moho also produces additional phases of waves as a result of diffraction and reflection. These phases are: PpPmp PpSmp, Ps, PpPms, and PpSms. The first three, PpPmp PpSmp, and Ps usually hit the seismograph within a few seconds of the initial, much larger wave, and are difficult to identify due to large amount of interference. However, the latter two, PpPms, and PpSms, can be identified and measured in the radial component of the P wave motion on the seismograph.[2]
Other time, several seismic events can occur in the same geographic area, with each event causing a corresponding vertical waveform and horizontal waveform. Once several observations have been collected, the waveforms can be aggregated into two synthetic seismograms, one for the vertical component and one for the horizontal component. The synthetic seismogram reduces random noise and makes it easier to see a pattern in the data. By visually inspecting the two waveforms, it is possible to deconvolute the data and identify each of the relevant phases of the P wave diffraction. With the timing of the phases, it is then possible to build a detailed model of the seismic velocities within the crust and determine the depth of the Moho at the location of the seismograph station.[2]
Applications
blah blah blah
- Obtain 3D view of seismic velocities in crust + mantle "crustal models"
- Useful into to support other seismological studies
- Can be used to get info from naturally occurring earthquakes as opposed to active experiments where seismic waves are triggered
- Also provides higher resolution results than active experiments
- Provides a 3D picture rather than cross-sections like CSS (controlled source seismology)[1]
- Example: find depressions in the moho below mountains
- Understanding more about earthquakes (which can cause disasters)[3]
References
- C. A. Langston: Structure under Mount Rainier, Washington, inferred from teleseismic body waves, J. Geophys. Res. 84(B9), 4749–4762, 1979.
- Charles J. Ammon, George E. Randall, and George Zandt: On the Nonuniqueness of Receiver Function Inversions, Journal of Geophysical Research 95(B10), 15303–15318, 1990.
- Frederiksen, A. W., and M. G. Bostock: Modelling teleseismic waves in dipping anisotropic structures, Geophysical Journal International 141, 401–412, 2000.
- Vinnik, L. P. (1977), Detection of waves converted from P to SV in the mantle, Phys. Earth Planet. Inter., 15(1), 39-45.
External links
- ^ a b Wiemer, S.; Agostinetti, N. Piana; Kissling, E.; Bianchi, I.; Spada, M. (2013-08-01). "Combining controlled-source seismology and receiver function information to derive 3-D Moho topography for Italy". Geophysical Journal International. 194 (2): 1050–1068. doi:10.1093/gji/ggt148. ISSN 0956-540X.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ a b c Langston, Charles A.; Burdick, L. J. (1977-06-01). "Modeling crustal structure through the use of converted phases in teleseismic body-wave forms". Bulletin of the Seismological Society of America. 67 (3): 677–691. ISSN 0037-1106.
- ^ Yamauchi, Makiko; Hirahara, Kazuro; Shibutani, Takuo (2003-01-01). "High resolution receiver function imaging of the seismic velocity discontinuities in the crust and the uppermost mantle beneath southwest Japan". Earth, Planets and Space. 55: BF03352463. doi:10.1186/BF03352463. ISSN 1880-5981.
{{cite journal}}: CS1 maint: unflagged free DOI (link)