Orlond's notes indicate that he brought a piece of equipment called a portable seismograph with him, but the device is nowhere to be seen.
The survey log shows that Orlond completed all his readings in the Thor Modan tunnel, save one labeled the 'east end of the exposed tunnel.'
The last entry in the log indicates Orlond tried to take refuge in the water and was attacked by subterranean threshers. They might've taken his equipment. You'll need to recover it before you can take the last reading.
You will be allowed to choose one of these rewards:
What did you find?
<Brugar looks over the report.>
This isn't good at all. Even if we could excavate the tunnels behind the blockage, there's no guarantee they wouldn't collapse again. It looks like some of these areas haven't been used in generations. We'll have to give Captain Gryan the bad news.
Jump in the water and kill threshers until the seismograph drops. Head east, place the seismograph on the bridge, then use it.