Geology 5640/6640 Introduction to Seismology 09 Jan 2015 © A.R. Lowry 2015 Read for Mon 12 Jan: S&W 1-28 Last time: Course overview Discussed: syllabus, resources, course objectives The observation: A seismogram is a record of ground motion (specifically, ground acceleration!) as a function of time Animations of vertical movement in EarthScope’s Transportable Array seismic network (for the Feb 2008 Wells, NV and several Gulf of California earthquakes)

Trabant et al. (2012) Seismol. Res. Lett. Various Gulf of California earthquakes,

What’s the point of showing this? Seismology provides crucial information about the nature of high energy seismic sources like earthquakes!

Finite fault model ( GEER_Post%20EQ%20Reports/ Baja%20California_2010/ Baja10_Ch02.html) M7.2 El Mayor- Cucapah Event (2010)…

Note however that earthquakes aren’t the only significant seismic energy source on the block!

A more familiar application of seismology, for most of you… Would be the application to imaging of the Earth’s subsurface

For example, seismic reflection* imaging as it is employed in exploration for petroleum and natural gas…

Seismic Reflections * *Sound waves reflect off of points in the subsurface where rock elastic properties change (  change in rock type, porosity, fluid, etc.). Energy returns are “migrated” to the approximate spatial location of the reflection source to form an image of the subsurface.

Example of subsurface imaging: thickness of the crust & seismic velocity ratio using P-to-S converted waves from distant earthquakes

Example of subsurface imaging: Upper mantle V P, V S and V P /V S ratios from waves from distant earthquakes (Schmandt & Humphreys, EPSL, 2010)