Part of the core from Japan's fault zone{credit}Japan Agency for Marine-Earth Science and Technology (JAMSTEC){/credit}
A mission to drill into the fault zone that caused the recent devastating earthquake in Japan has met with only partial success.
Researchers on board the Japanese drill ship the Chikyu were aiming to bore right through the plates that slipped during the massive 9.0 earthquake of 11 March 2011, pull up sediments and install temperature sensors down the hole. This, they hoped, would help to fill in some crucial blanks in models of earthquake behaviour — specifically, how much friction exists between sliding plates (see ‘Drilling ship to probe Japanese quake zone’). They got their core, but they didn’t manage to install the temperature sensors.
The problems were frustratingly simple: the cruise was repeatedly delayed by bad weather, and then the cable for their underwater viewing system malfunctioned, leaving drillers unable to see what they were doing. “This was the first time drilling was happening in such deep water,” says James Mori, a seismologist at the Disaster Prevention Research Institute of Kyoto University in Japan and joint chief of the expedition. “Such problems aren’t unexpected. Things happen when the pressure is that high.” Each time something went wrong, he notes, it would take about three to four days for the drilling rig to be pulled up and put back down again through 7 kilometres of water. “It was very frustrating. Very disappointing.”
Nevertheless, the team is celebrating: they set a new record for drilling in deep water (see ‘Drilling into Japan’s quake zone‘) and extracted core samples from 648–844.5 metres below the seabed, right across the fault zone as hoped (see press release). As usual, some parts of the core crumbled and were lost before they could be pulled on board — they retrieved about 40–50%. This is actually a good hit rate for this sort of mission, but it means the team doesn’t yet know whether they have core samples from the crucial bit that slid during the recent quake. Either way, the cores should help to shed light on the physical properties of fault-zone sediments, says Mori.
The researchers haven’t yet given up on the idea of taking the fault’s temperature. It looks like they might be able to get another slot on the Chikyu in July or August, says Mori. They can reuse the same wellhead, but will drill a new hole and try to get the temperature sensors down again. That means their temperature record will start months later than hoped, but it shouldn’t be too late to be useful, he says.
