Ultraprecise compaction and vertical strain measured in the Mississippi River Delta using Optical Fiber Strainmeters

We are using tensioned optical fibers for the ultraprecise measurement of Earth strain in the Mississippi River Delta, where high subsidence rates threaten a large area with flooding from the Gulf of Mexico. As part of a "superstation" near Myrtle Grove, Louisiana (established with funding from the U.S. Army Corps of Engineers), we have instrumented two boreholes, 10 m and 40 m deep, with interferometric optical fiber sensors. These continuously record the vertical displacements of surface monuments to cemented-in anchors at depth. GPS stations attached to the same surface monuments tie the local compaction measurements to an absolute reference frame. These measurements, with a planned installation at an intermediate depth, will allow us to partition the subsidence between layers at various levels above the Pleistocene basement. Correlating tidal loading and vertical strain, and comparing vertical strain from distant teleseisms, reveals variations in local properties with depth.