ÖNCEL AKADEMİ: SOLID EARTH GEOPHYSICS
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Seismic Waves and Earth’s Interior
![Solid Earth Geophysics-Geop503 Ali Oncel [email_address] Department of Earth Sciences, KFUPM Seismic Waves and Earth’s Interior Reading: Fowler Chapter 8- Section 8.1](https://image.slidesharecdn.com/lecture04-091219225439-phpapp01/85/ONCEL-AKADEMI-SOLID-EARTH-GEOPHYSICS-1-320.jpg)
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ÖNCEL AKADEMİ: SOLID EARTH GEOPHYSICS
- 1. Solid Earth Geophysics-Geop503 Ali Oncel [email_address] Department of Earth Sciences, KFUPM Seismic Waves and Earth’s Interior Reading: Fowler Chapter 8- Section 8.1
- 2. Mysteries of the Inner Earth http://ourworld.compuserve.com/homepages/dp5/inner1.htm
Notas do Editor
- Lehman 5144 Fe solid against FeO, FeS fluid (inner/outer core boundary) Gutenberg: 2885, it was discovered by Oldham but corrected depth for this discontinuity was carried out by Gutenberg. D'' 2870 thin, mixing of mantle and core material? (D”=D double-prime) 670 km 670 worldwide, no earthquakes deeper, debates over whether a composition, phase, or viscosity change 400 km 400 worldwide LVZ 50-200 regionally variable depth Moho 4-55 (abbreviation of Mo-ho-RHO-vi-chik) - sharp compositional change Conrad ? 5-30 mafic to felsic crust, often absent
- Richard Dixon Oldham Richard Dixon Oldham ( July 31 , 1858 – July 15 , 1936 ) was a British geologist who, in 1906 , argued that the Earth must have a molten interior as S waves were not able to travel through liquids nor through the Earth's interior. Inge Lehmann Inge Lehmann ( May 13 , 1888 – February 21 , 1993 ), Fellow of the Royal Society ( London ) 1969 , was a Danish seismologist who, in 1936 , argued that the Earth must not only have a molten
- Ray paths for PKIKP, the direct P-wave passing through the mantle, outer core and inner core (1959). pp.254-Richter-1959 The surface of the core, when finally found by Gutenberg, proved to be halfway down to the center. Nevertheless, the core is large; it is larger than the planet Mars, and its radius is a little greater than diameter of the moon.
- As the angle of incidence at the hypocenter decreases, the rays descend more steeply and to greater depth and emerge at the surface at increasing distance. When the distance corresponds to a central angle of about 103 between hypocentre and station (for ordinary shallow earthquakes) the P ray grazes the core. P waves are refracted at the Mantle-Outer Core interface S waves are stopped at this interface Both create shadow zones and S wave attenuation implies a fluid outer core
- After Bolt (1982)
- Richter-1959-pp.256 As the angle of incidence at the hypocenter decreases, the rays descend more steeply and to greater depth and emerge at the surface at increasing distance. When the distance corresponds to a central angle of about 103 between hypocenter and station (for ordinary shallow earthquakes) the P ray grazes the core. Beyond this distance the amplitude of recorded P decreases rapidly; but there is not a sharp shutting off; and P-waves, especially of long periods, continue to be recorded up to angular distances of at least 130. This is a wave phenomenon not explained in terms of geometrical optics; it corresponds to diffraction of the P waves round the core boundary, analogous to the diffraction of light into a shadow. The effect for S is even stronger, but not so easy to observe. PKP: At the angle of incidence for which P grazes the core, the first refracted wave enters the core and the resulting ray is the first for PKP (P’). It emerges at the central angle about 10 deg . In excess of 180. Because of symmetry, a wave of this type appears at all points distant 10 deg from the antipodal “ on the opposite side or sides of the earth ” point, or at 170 degrees.