Phase Two: JC114

On Thursday morning the second stage of the OSCAR cruises began, with the start of cruise JC114. The James Cook set sail once again, this time with an (almost) completely different set of crew, technicians, scientists and equipment. We're spending another 6 weeks in the Panama Basin, this time to acquire our seismic data over the Costa Rica Rift, and the ODP borehole 504B, a section drilled ~1350 m into the oceanic crust.

The Cook alongside in Caldera, Costa Rica

Active seismology uses acoustic (sound) pulses to try and acquire an idea of the properties and structure of the Earth's crust and interior. We will be letting off these pulses using equipment towed behind the ship, which will travel down to and through the seabed, reflecting and refracting off layers of different materials as they go. We then record the pulses that come back to the ship after going through the crust, using receiver sensors called 'hydrophones' which detect these acoustic vibrations. Our sensors are deployed in two different ways: towed behind the ship will be a 1.5 km hydrophone streamer, mostly for recording the reflection data; and then we will also deploy 75 ocean-bottom seismographs (OBSs) to sit on the seafloor, predominantly for wide-angle refraction data.

Up to now, we have deployed four OBSs on the Sandra Ridge, in collaboration with Colombia, to passively monitor seismic activity (earthquakes!) that may occur in that area. We have then steamed to the Costa Rica Rift, and have deployed our OBSs in this area in a grid format over the rift. After some more equipment deployment this afternoon and through the night, we will hopefully begin sending our acoustic pulses tomorrow morning and the data will begin streaming in!

Dolphins seen whilst still on the continental shelf

Wildlife update
We've been lucky enough to have a few sightings of dolphins already on this trip, and even a possible whale seen in the distance from its blow. A group of dolphins saw the ship out of the Gulf of Nicoya when leaving Caldera, and a pod of bottle-nosed dolphins were riding the bow wave yesterday afternoon. More unexpectedly, we've found some terrestrial stowaways on board, including several large crickets which are providing some tropical background noise in the hangar at night.