Day Two

It was great to be out. Both Ellen and me think of ourselves as field scientists, so it was always much more fun being out in the wilds rather than being cooped up in the workshop. Still, it meant we’d not much idea how the others were getting on with their challenges. And, as we were about to find out, nature can throw up some real surprises.

From the air, by far the best scarp along the line of the fault had been just west of the town of Lone Pine. On the ground, this was a beautiful 3 m high cliff is cut in coarse rocky debris coming down from the adjacent Alabama Hills as what geologists call an alluvial fan. And that’s when things got a little tricky. You see, a 3 m high scarp implies a really big earthquake, and there was something else to consider. Small dry channels coming down to the fault appeared to have been shifted sideways on crossing it. To me, that was a clear sign that this fault was not just moving vertically, but also horizontally. And the amount of horizontal slip seemed much more that the vertical. In one clear place, we measured as much as 20 m of sideways offset. If this was all just our 1872 it must have been truly enormous. But what was more likely to me was less appealing to the production team – our scarp was the product of not just one earthquake (1872) but also of several earlier ones as well. We needed to take a lot of careful measurements here. Measuring slope profiles (literally the change in gradient down the cliff) showed Ellen and I that there was a steep 1 m high section in the centre of the more rounded scarp. It was this 1 m high scarplet that I thought was the 1872 ground rupture.

The story was getting very complicated. If the 1 m high scarp was the 1872 event, then the full 3 m high scarp was the result of this and, assuming earlier events were of a similar size, two previous events. If that was the case, then our 20 metres of horizontal slip was similarly the result of three movements, each of around 7 m. It all looked very tenuous and speculative to the production team, particularly given that in the final programme there would only be two or three minutes to get all this over to the viewer. Still, my job wasn’t to make the complex natural world fit a nice simple television story – that was their job.