Iain's Aerial Surveyor Diary

Production team

Day One

At last – something I’m really familiar with - earthquakes. It’s what I’ve been specialising in as a geologist over the last ten years or so. But even with that the challenge is still daunting. Kate has given Ellen and me the task of finding the epicentre of an earthquake that struck the area in 1872 and to estimate its size on the Richter scale. In strict terms, the first part is impossible – the epicentre of an earthquake is something that is determined by seismic-recording instruments (seismographs) or is inferred from piecing together a picture of where earthquake damage to buildings was greatest. Arriving on the crime scene 130 years later, we’ve got neither of those. A quick plea to the production team – can our task be to simply find the ‘centre’ of the earthquake, which is more vague, rather than the epicentre, which is an impossible holy grail. It is agreed, and though it will still be problematic, Ellen and I start planning.

Now the normal way you’d approach this is to get hold of lots of maps, air photos and satellite images of the area around us to look for the tell tale signs of earthquake. What we’d be looking for are natural straight lines in the landscape, since earthquake cause long cracks, or faults, within the Earth’s crust to rupture and if there’s enough energy available in the quake, the rupture makes it all the way to the ground surface, breaking through as a cliff or scarp. And in our desert landscape these features are often amazingly clear, first because they aren’t eroded away very fast and secondly because the faults are often pathways for water to move up so they appear as areas of moisture on the land surface. That’s where Ellen’s knowledge of vegetation will be great. So in the absence of high-tech images, what we really need to do is get up high and look down on the land. The production team have second guessed us here – they’ve already arranged for a small plane to fly us around if we need it. We do, and we’re off.

Now I don’t normally throw up in planes. And I certainly didn’t plan to chuck up when we’re flying low along an earthquake fault – my dream job. But by the end of two flights I’m face down in a sick bag revisiting my Alabama Hills salad. The trip had started great – from the flat dried flats of Owens Lake we spotted the clear, straight cliff that is so typical of earthquake faults in this region, and we followed it north through Lone Pine and then past Independence. Here it seemed to follow a line of ponds just west of the Owens River. Further north it was even clearer, a high cliff that cut through and displaced small volcanic cones near the town of Big Pine. After that we lost it. Of course, after we spotted the trace of the fault, we had to show it to the camera crew, so up I went again with cameraman Keith and sound recordist Robbie. They’d previously had the pleasure of recording me urinate (programme 1, day 1) but I think that even that was preferable to the sight of me throwing up as the pilot rolled the plane sideways to let Keith get a shot straight down on the fault line. Keith of course missed the action but Robbie, hooked up to me for sound, had no such luck. A very white and sheepish earthquake geologist came off the plane – I think we should stick to looking for this thing on the ground.

Deciding that we should look for where movement on the fault was greatest as the most likely candidate for the centre of the earthquake, Ellen and I jump into the landrover to find where the land surface is most disrupted. This is real detective stuff, because tracking the fault on the ground is much tougher than from the air. The line of pools of water are found almost at the mid-point of the fault (which from our flight we figured was almost 100 kilometres long), but here there was little in the way of direct signs of faulting. The low scarp that runs along one edge of the ponds was probably the fault (it was in the right place) but I was worried that it might also be simply the natural cliffed edge of the Owens River flood plain. We just hoped that in Day 2, things would be much clearer.

There’s another problem. Mike had asked about where to find calcium carbonate and I gave directions to the lovely layered limestone cliffs where we collected the gypsum (and calcite) veins in programme 2. But the curse of the limestone appears to be continuing, since Mike tells me that he doesn’t think that its really limestone. Not knowing if he’s collected it from the right point it’s hard to say, but it is possible that the limestone has been baked and chemically changed by heat and pressure, to make what geologists call a metamorphic limestone. So, after a few beers chatting into the night, we head for bed to mull over our various dilemmas.

Production team

Day Two

It was great to be out. Both Ellen and I 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 3m high cliff 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 3m 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 20m 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 1m high section in the centre of the more rounded scarp. It was this 1m high scarplet that I thought was the 1872 ground rupture.

The story was getting very complicated. If the 1m high scarp was the 1872 event, then the full 3m 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 7m. 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.

Production team

Day Three

It was a nice break from the rigours of the earthquake story to start the final day with the air balloon test. Ellen and I have been hearing rumours of billowing bin bags that never really take off, so when we join mission control for the lift off we’re not sure what to expect. In the end it was great fun. Just as we got there with Mike, we could see Jonathan and Kathy desperately trying to keep the balloon in check. In the end it took off before we or most of the camera crew could get there – frustration for Kathy and Jonathan who now needed to have a repeat performance of their only success of the last couple of days. There was no need to worry – right on cue the balloon took off carrying its camera payload. The relief for all of us was clear as we danced around like idiots below. God knows what the pilot of a low-flying F-16 thought as he buzzed us.

Still, it was just putting off the inevitable for Ellen and I. Kate was pressing for an answer for our challenge. Some decisions had to be made. In the end, we plumped for the assumption that since the biggest ground movements were in the vicinity of Lone Pine then that was a reasonable guess for where the centre of the 1872 quake was. The magnitude was more tricky. Did we assume just one great quake and use the values of 3m vertical and 20m horizontal, or did we go for a more geological assumption of three large quakes with 1m vertical and 7m horizontal, the most recent of which was our 1872 event. It’s at times like that that you see the faces of your academic peers bearing down on you, and that it is the most likely reason for me opting for the more cautious choice. So, a slip value of 7.5m was added to a fault length of 100km and inserted into a standard geological calculation that also assumed that the fault extended down into the Earth for 15km and that the rocks had a particular coefficient of friction – basically a measure of how easy they are to break. The result is what seismologists refer to as moment magnitude, which isn’t the same as what Kate asked for – Richter magnitude. Since Richter magnitude is based on the record that the seismic waves have on a seismograph, it is impossible for us to determine that. But thankfully, at moderate and large quakes the moment magnitudes are roughly comparable to Richter magnitudes, so we could just assume a straight conversion between the two.

So, our answer to Kate was a magnitude of 7.6 and a location close to Lone Pine. To be honest it was a best guess with what we had, so I wasn’t that confident as Kate opened the envelope. Then, hearing that the answer was supplied by legendary earthquake geologist Burt Slemmons, I knew that I wasn’t going to be in a position of contesting the result. In the end Burt placed the centre of the quake a bit further north, roughly mid-way along the fault (maybe that would just have been a simpler way to do it) but gave a lovely magnitude range of 7.5-8.0. Given that the magnitude scale is logarithmic, so a magnitude 8 event is ten times larger than a magnitude 7, that is a fairly generous range, but it is all because we’re talking about a quake that happened 130 years ago before modern seismic measurements. Given the time we had, I don’t think Ellen and I did that bad.

And neither did Mike. We hadn’t witnessed the torture that Mike had gone through trying to get his carbon dioxide filter to work with the dodgy limestone, but it was clear that he really wasn’t sure if this was going to work. In fact, in previous series the Mike’s chemistry was famed for its glorious failures. This series, however, he was on a roll, and so it was brilliant to see that this was no exception. A glorious success. And it was nice to see chemistry taking centre stage at the finale of a Rough Science programme.