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.