![Assume a flat earth with crustal thickness of 35 km and average crustal and upper mantle](https://www.gkseries.com/blog/wp-content/uploads/2023/10/Assume-a-flat-earth-with-crustal-thickness-of-35-km-and-average-crustal-and-upper-mantle.jpg)
Q. Assume a flat earth with crustal thickness of 35 km and average crustal and upper mantle P-wave velocities of 6.4 km.s–1 and 8.1 km.s–1, respectively. The minimum distance from the epicenter of a near surface earthquake at which Pn-waves are observed is__________km.