The earthquakes in 1 and 10 must be the same earthquake, because 10 shows the same time period from Bron's perspective. Of course, it is possible that they are different earthquakes, but this just complicates the story and doesn't give it any additional explanatory power. So, until evidence to the contrary surfaces, one earthquake it is.
While the sun is a far more energetic force than the hot interior of our planet, the sun damages the land horizontally, spending almost all its energy into turning layer after layer of ground to sand. This is a very energy-intensive process. Only a very small portion of this energy goes deeper into the ground, so the sun is very bad at making cracks in the ground. The deepest cracks in very dry land can be up to a few meters deep. On the other hand, earthquakes, though containing minuscule amounts of energy compared to the total energy of light that hits the Earth's surface, damage the land vertically, and crack through kilometers of rock. So, the tiny cracks made by the sun will be of little to no help to earthquakes when they make their own cracks.