Near-Podal Observations of PKPPKP Waves and Implications for Central Inner Core Structure-fig.2

Near-Podal Observations of PKPPKP Waves and Implications for Central Inner Core Structure-fig.2 Figure 2. Vertical components of the Kyrgyz Seismic Telemetry Network records bandpassed between 0.2 and 1.0 Hz for an earthquake near the Afganistan-Tajikistan border. PKPPKPdf waves arriving at a steep incidence angle are visible at all records.
<br /><br />
The amplitude and radial dependence of hypothesized inner core anisotropy are not well known. Apart from previously observed complexity in geometry, some recent results suggest changes in anisotropic properties in the regions of the inner core close to the planetary center. With the spatial distribution of large earthquakes and current configuration of seismographic stations worldwide, it is difficult to achieve sampling of the deep interior of the inner core, except for paths nearly parallel to the equatorial plane. Figure 1 demonstrates this property. Even if a large earthquake occurs at extreme latitudes, say at -50°s, although possible to find antipodally positioned locations on the globe, such geometries could not produce angles between the PKP leg and the Earth’s rotation axis (ksi) smaller than 35 degrees. This makes interpretation of anisotropic properties near the planet’s center, at a minimum, very challenging.
<br /><br />
PKPPKP and even more exotic seismic waves are used to examine inner core structure. Breger et al. (2000) reported that the travel times of PKPPKP waves recorded at NORSAR network with polar geometries sampling the top 400 km of the inner core were not anomalously advanced. The near-podal PKPPKPdf waves show much promise for studying inner core structure. Figure 2 illustrates an example of one near-podal PKPPKPdf observation, recorded by the Kyrgyz Seismic Telemetry Network for an Afganistan-Tajikistan border earthquake. Preliminary results from analyzing near-podal PKPPKPdf travel times suggest that the central part of the inner core is not fast in the direction parallel to Earth’s axis, which is in contradiction with presently hypothesized anisotropy models. Painstakingly collected data points from near-podal PKPPKPdf travel times will thus have very important implications for our understanding of the anisotropy and other properties of the deep inner core.
<br /><br />
Breger, L., B. Romanowicz and S. Rousset, New constraints on the structure of the inner core from P’P’, Geophys. Res. Lett., 27, 2781-2784, 2000.

Comments

No comments yet.

  •  

Welcome

Welcome to the IRIS Image Gallery – a diverse collection of photographs and visuals that encompass the range and breadth of seismology and the seismological community.

Please browse through our albums. These low and medium-resolution images can be freely used for personal and educational/academic purposes, but we request you recognize the image contributor by including in your product or presentation the credit displayed with each image.

More information is available in the Image Use Agreement.

If you have any comments, questions, or suggestions related to the IRIS Image Gallery, you can send them to gallery@iris.edu.

Photo info

Popular tags