Why Should I Care About Your Slop? Linking Shallow Geologic Observations to Deeper Earth Processes

Rich Briggs, US Geological Survey

Geoscientists draw on many powerful tools and techniques to document surface deformation. Ideally these observations help illuminate deeper Earth processes. However, the resolution and uncertainty of geologic observations may fail to discriminate between alternative geophysical models; conversely, geophysical models can struggle to match the richness - or is it "slop"? - of surficial measurements. I will draw on work in Sumatra, Haiti, Alaska, and Pakistan to discuss examples where relatively low precision, but well-placed surficial observations are critical for differentiating geophysical models. In my own field of earthquake geology I suggest that as rapid imaging and geodetic differencing techniques become routine, the role of the field investigator will evolve away from primary observer toward opportunistic discriminator. That is, documentation of gross anatomies - such as earthquake rupture location or length - are becoming less important than discerning features that sensors may not be able to resolve, and which might prove critical for rejecting alternate hypotheses about deep processes. Relevant examples will include coastal uplift measurements for fault slip inversions; on- versus off-fault deformation measurements from large surface ruptures; and geologic versus geodetic slip rate investigations. In the best circumstances, modelers and field teams work closely before and during fieldwork. Similarly, field teams, especially in response mode, deploy with remote sensing data and preliminary geophysical models already in hand.