**6. Conclusions**

The variation of crust corrected travel time residuals correlate well with our estimates of crustal and lithospheric thicknesses in the study region. The large negative

**41**

provided the original work is properly cited.

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

\*Address all correspondence to: prantikmandal62@gmail.com

*P-Wave Teleseismic Tomography: Evidence of Imprints of Deccan Mantle Plume…*

residuals are found to be associated with the Kachchh and Cambay rift zones, which are characterized by a marked crustal and asthenospheric thinning while positive

Our tomograms reveal a distinct low dVp anomaly at 50–170 km depths underlying the central Kachchh rift zone. However, this anomaly vanishes for deeper regions (>210 km) due to poor ray sampling. At 90–130 km depths, the resulting tomographic model reveals a slower P-wave speed on the eastern part of Kachchh compared to that of the western part. A slow dVp anomaly is mapped at 50–170 km depths below the central KRZ, which is also characterized by the crustal as well as lithospheric thinning and negative traveltime residuals. This upper mantle low dVp anomaly could be attributed to the presence of carbonatite/partial melts related to the Deccan volcanism of 65 Ma. We propose that the volatile CO2, which is emanating from the crystallization of carbonatite melts in the asthenosphere, is playing a crucial role in generating lower crustal earthquakes occurring in the Kachchh rift

The checkerboard test results suggest that our tomographic model is quite well resolved for the central KRZ at 50–170 km depths while tomographic model at more than 210 km depth is poorly resolved due to poor ray sampling. The checkerboard test reveals that 85–90% of the synthetic velocity anomaly could be retrieved at 50–170 km depths below the central KRZ (**Figure 4e**–**h**). Thus, the velocity model below the KRZ seems to be well-resolved. However, the retrieval of synthetic velocity for the surrounding regions are not very good (<80%). To increase the resolution of the tomographic images of the upper mantle velocities, a future study could be planned to combine Kachchh dataset with those from other broadband stations in Gujarat and Rajasthan, using more teleseismic events with epicentral distances

and back-azimuths between 180 and 270o

The author is grateful to the Director, Council of Scientific and Industrial Research—National Geophysical Research Institute (CSIR-NGRI), Hyderabad, India, for his support and permission to publish this work. This study was supported by the Indo-Czech (CSIR-ASCR) collaborative project no, IND 2012/19.

.

*DOI: http://dx.doi.org/10.5772/intechopen.83738*

residuals describe the unrifted regions.

zone [18].

between 30 and 90o

**Acknowledgements**

**Author details**

Prantik Mandal

CSIR-NGRI, Hyderabad, India

*P-Wave Teleseismic Tomography: Evidence of Imprints of Deccan Mantle Plume… DOI: http://dx.doi.org/10.5772/intechopen.83738*

residuals are found to be associated with the Kachchh and Cambay rift zones, which are characterized by a marked crustal and asthenospheric thinning while positive residuals describe the unrifted regions.

Our tomograms reveal a distinct low dVp anomaly at 50–170 km depths underlying the central Kachchh rift zone. However, this anomaly vanishes for deeper regions (>210 km) due to poor ray sampling. At 90–130 km depths, the resulting tomographic model reveals a slower P-wave speed on the eastern part of Kachchh compared to that of the western part. A slow dVp anomaly is mapped at 50–170 km depths below the central KRZ, which is also characterized by the crustal as well as lithospheric thinning and negative traveltime residuals. This upper mantle low dVp anomaly could be attributed to the presence of carbonatite/partial melts related to the Deccan volcanism of 65 Ma. We propose that the volatile CO2, which is emanating from the crystallization of carbonatite melts in the asthenosphere, is playing a crucial role in generating lower crustal earthquakes occurring in the Kachchh rift zone [18].

The checkerboard test results suggest that our tomographic model is quite well resolved for the central KRZ at 50–170 km depths while tomographic model at more than 210 km depth is poorly resolved due to poor ray sampling. The checkerboard test reveals that 85–90% of the synthetic velocity anomaly could be retrieved at 50–170 km depths below the central KRZ (**Figure 4e**–**h**). Thus, the velocity model below the KRZ seems to be well-resolved. However, the retrieval of synthetic velocity for the surrounding regions are not very good (<80%). To increase the resolution of the tomographic images of the upper mantle velocities, a future study could be planned to combine Kachchh dataset with those from other broadband stations in Gujarat and Rajasthan, using more teleseismic events with epicentral distances between 30 and 90o and back-azimuths between 180 and 270o .
