Getting your Feet Wet - Why seismologists acquire simultaneous onshore/offshore data
Most major plate boundaries (with a few notable exceptions, can you think of which they are?) sit either completely offshore (i.e. mid-ocean ridges) or at the junction between an ocean and a continental land mass (i.e. subduction zones). Thus to study the forces that control plate tectonics we commonly have to jump in and "get our feet wet" - i.e. go into the oceans. As seismologists we routinely get our feet wet by deploying ocean-bottom seismometers (OBS) to record ground motions both from near and far earthquakes as well as man-made sources.
However, what if our scientific target calls for a combination of "dry" and "wet" tactics (apologies if you've lost the metaphor now ...) i.e. onshore and offshore instrumentation? Perhaps your investigating the continuation of a downgoing oceanic slab under North America or , as in my case, your investigating early-stage continental rifting beneath rift lake. Then it's time to dust off your sea-going legs and your 4x4 driving skills as you're going to want to deploy instruments both in the oceans and on the mainland. In fact these combined experiments are increasingly common nowadays as scientists become more familiar/comfortable deploying OBS and also with national agencies highlighting the scientific priority of subduction and rift processes.
Ok, that was a super long introduction to what this post is actually about - cutting SEGY data from continuous data! If you don't understand a lick of this then just hold on for the next post as we'll get there, I promise. In my work we had 57 onshore stations located around Lake Malawi that recorded the airgun blasts that we shot in the lake as a part of the active-source experiment. Thus we want to use these onshore stations just like the OBS and create receiver gathers with them to constrain sediment and crustal structure. But wait - how do we do that? How does one cut SEGY data from continuous data? Get ready lucky reader as I will lay out all the nitty gritty details in my next post.