Surface rupture mapping in Burnham Camp meet with Humboldt ALumni!

Monday 9-27 

We are staying in the suburbs of Christchurch in an area called Riccortan. At this location we are about 20 km from the area of maximum horizontal displacement, Burnham Camp. That is where we spent yesterday and today. We decided that it would be interesting to get an even higher resolution scan of a small section of the surface rupture to capture all of the detail, the small faults, uplifts, and fractures that comprise the very complex rupture pattern. Garth and Rob, GNS Science, set up the LIDAR to scan an area of about 50 × 50 m in dimension. The scanner rotates 360° and fires a laser (it looks like a really fancy table-top digital scanner) that collects about 15 million data points at each station. For this experiment it was moved about 6 times so they have collected about 90 million data points of the ground surface! To supplement this information, Paul used the Real-Time Kinematic GPS to make small features, mainly fractures, that have no vertical relief on them that the scanner might not see. Additionally, Rob created a sketch map (old-fashioned geology) of the scanner study just to see how accurate the old method is compared to the high-tech method.

It should be noted that this part of South Island, along the eastern coast, is referred to as the Canterbury Plain, a flat and vast sheet of post-glacial outwash gravels that is 40 to 50 km wide and extends for more than 200 km along the east coast of the island. Great rivers, such as the Rakaia and Waimakariri, carry enormous amounts of sediment from the Southern Alps and their eastern ranges toward the ocean to produce this plain. It is thought that the age of the surface (except for the active river areas) is on the order of 14,000 to 16,000 years old. That age corresponds with the best estimate for the last glacial maximum for South Island. For the most part, the Canterbury Plain has little relief on it. Thus, unlike many western US fault ruptures that break across hills, mountains, valleys, etc., this fault has broken across a nearly flat datum. It stands out very clearly.

I got to hike WSW along the rupture to explore more of the details of this fault. As the fault makes small turns and jogs, the nature of the surface rupture changes. In some locations it suddenly dies out and then steps a few hundred meters, where it continues on. A large high-tension electrical transmission line traverses the rupture. One of the towers was moved more than 3 m with respect to the two towers on either side of it. The only evidence for this motion was the tension of the power lines. To the north, the towers moved closer together and the lines sagged. To the south, the towers moved apart and the lines are now quite tight and straight. Remarkably, the towers withstood the strong ground shaking and surface displacement with failing and the high-tension lines are still producing energy. I’m sure, at some point, the electrical company will make some adjustments to the lines.

Prior to coming to New Zealand I got an email from Rebecca Teasley, who said that her mother sent a copy of the Humboldt press release announcing that Paul and I were headed to Christchurch. She said that she and her husband, John Allen, were Humboldt natives and Humboldt graduates now living in Christchurch. In fact, John was in my first geomorphology class. They are both graduates of the Humboldt Environmental Resources Engineering program at Humboldt. Becky is finishing a post-doctoral program at Canterbury University. We met this evening in old, downtown Canterbury for dinner and beers. What an amazing thing to walk in and see John after all these years! John is a geotechnical engineer and has been working closely with the Geo-Engineering Earthquake Reconnaissance (GEER) team that flew in shortly after the event to document the earthquake damage. John and Becky got out into the field almost immediately after the main shock and got great photos of the surface rupture. The highway department here was amazingly quick to start repairing damaged roads so John and Becky’s photos are going to prove to be a great resource. It was sure a pleasure getting together with them to talk about the event, and, of course, Humboldt!

We also met with Dr. Mark Quigly, a geology lecturer with Canterbury University, and Dr. Kevin Furlong, professor at Penn State University. Mark has been directing much of the on-the-ground activity. Kevin was here on sabbatical. I don’t envy Mark’s schedule trying to get students into the field, dealing with the onslaught of visiting scientists and teaching at the same time! The Canterbury folks are doing an incredible job!

It was a long day. Tomorrow we are spending the morning toward the western end of the rupture near Horarata. They had ground accelerations there that approached 1g. In the afternoon we are meeting with Kevin and one of Mark Quigly’s students in Christchurch to look at evidence for boulders having been thrown out of the ground. This evening we meet with Mark Stirling (GNS Science) who will be presenting a talk on the hazards mapping projects he has been conducting for New Zealand.

As we have travelled through Christchurch we have noticed that the damage is extensive. There are many brick (unreinforced masonry) buildings, many of which have damage but many that do not. John Allen was saying that those buildings that had even minimal seismic structural upgrading seemed to perform pretty well while almost all that failed had no seismic retrofitting.