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When there are many adjacent seismograph stations, it is possible to "stack" receiver function data across seismograph stations to build a 2D or even 3D model of the depth of the Moho.<ref name=":3">{{Cite journal|last=Rondenay|first=Stéphane|date=2009-10-01|title=Upper Mantle Imaging with Array Recordings of Converted and Scattered Teleseismic Waves|url=https://doi.org/10.1007/s10712-009-9071-5|journal=Surveys in Geophysics|language=en|volume=30|issue=4|pages=377–405|doi=10.1007/s10712-009-9071-5|issn=1573-0956}}</ref> This is possible because each station can determine the depth of the Moho at its own location (essentially a 1D measurement). Data from multiple individual data points from adjacent stations can be grouped together either via surface distance or via common conversion points. This data is then plotted side by side to create a unified graph of the Moho depth over a given area.<ref name=":3" /> |
When there are many adjacent seismograph stations, it is possible to "stack" receiver function data across seismograph stations to build a 2D or even 3D model of the depth of the Moho.<ref name=":3">{{Cite journal|last=Rondenay|first=Stéphane|date=2009-10-01|title=Upper Mantle Imaging with Array Recordings of Converted and Scattered Teleseismic Waves|url=https://doi.org/10.1007/s10712-009-9071-5|journal=Surveys in Geophysics|language=en|volume=30|issue=4|pages=377–405|doi=10.1007/s10712-009-9071-5|issn=1573-0956}}</ref> This is possible because each station can determine the depth of the Moho at its own location (essentially a 1D measurement). Data from multiple individual data points from adjacent stations can be grouped together either via surface distance or via common conversion points. This data is then plotted side by side to create a unified graph of the Moho depth over a given area.<ref name=":3" /> |
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TODO: further discuss H-k stacking + common conversion point stacking (ie what are common conversion points) |
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TODO: Add a diagram of an incident wave hitting the Moho |
TODO: Add a diagram of an incident wave hitting the Moho |
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Revision as of 00:47, 10 March 2019
Article to improve: Receiver function.
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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.[1] 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.[2] The resulting waveform is the receiver function.
Similarly, a teleseismic S-wave will generate an S to P conversion beneath the seismic station.
Method
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. (See seismic phase notation for more info). 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.[3]
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.[4] Receiver functions use Snell's law with wave refraction and reflection from P waves in the mantle to estimate the depth of the Moho. Because of this they can only be generated properly if the central angle between the seismic event and the seismograph station is between 30 and 80 degrees.[3] 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.[3]
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 seismic station.[3]
Stacking
When there are many adjacent seismograph stations, it is possible to "stack" receiver function data across seismograph stations to build a 2D or even 3D model of the depth of the Moho.[5] This is possible because each station can determine the depth of the Moho at its own location (essentially a 1D measurement). Data from multiple individual data points from adjacent stations can be grouped together either via surface distance or via common conversion points. This data is then plotted side by side to create a unified graph of the Moho depth over a given area.[5]
TODO: Add a diagram of an incident wave hitting the Moho
Applications
Receiver functions provide detailed information on the seismic velocities within the crust and on the depth of the Moho at a specific location. This data alone can be useful in obtaining information about a specific location.[3] But when receiver function data from one seismic station is combined with data from many other stations, it is possible to build a detailed map of the Moho depth and of seismic velocity across a large geographic area.
This data can be used for a variety of purposes. It can be used to note variations in the depth of the crust. Receiver functions have been used, for example, to discover depressions in the Moho below mountains in southwest Japan.[6] This data can also be used to better understand earthquakes that cause natural disasters.[6] Additionally, maps of seismic velocities and crustal depth are useful as baseline data for additional seismological studies.[4]
Data from receiver functions can also be used in conjunction with data, such as data from controlled source seismology (CSS) to provide higher resolution 3D maps of the Earth's crust.[4]
References
- ^ Vinnik, L.P. (1977-9). "Detection of waves converted from P to SV in the mantle". Physics of the Earth and Planetary Interiors. 15 (1): 39–45. doi:10.1016/0031-9201(77)90008-5.
{{cite journal}}: Check date values in:|date=(help) - ^ Frederiksen, A. W.; Bostock, M. G. (2000-05-01). "Modelling teleseismic waves in dipping anisotropic structures". Geophysical Journal International. 141 (2): 401–412. doi:10.1046/j.1365-246x.2000.00090.x. ISSN 0956-540X.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ a b c d e 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.
- ^ a b c 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 Rondenay, Stéphane (2009-10-01). "Upper Mantle Imaging with Array Recordings of Converted and Scattered Teleseismic Waves". Surveys in Geophysics. 30 (4): 377–405. doi:10.1007/s10712-009-9071-5. ISSN 1573-0956.
- ^ a b 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)