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Abstract
Geodetic data from the Global Navigation Satellite System (GNSS), and from satellite interferometric radar (InSAR) are revolutionizing how we look at instantaneous tectonic deformation, but the significance for long-term finite strain in orogenic belts is less clear. We review two different ways of analyzing geodetic data: velocity gradient fields from which one can extract strain, dilatation, and rotation rate, and elastic block modeling, which assumes that deformation is not continuous but occurs primarily on networks of interconnected faults separating quasi-rigid blocks. These methods are complementary: velocity gradients are purely kinematic and yield information about regional deformation; the calculation does not take into account either faults or rigid blocks but, where GNSS data are dense enough, active fault zones and stable blocks emerge naturally in the solution. Block modeling integrates known structural geometry with idealized earthquake cycle models to predict slip rates on active faults. Future technological advances should overcome many of today's uncertainties and provide rich new data to mine by providing denser, more uniform, and temporally continuous observations.
Highlights
Structural geologists have alw ays w anted to stud y the grow th of structures in real tim e: how d o limbs of fold s rotate? H ow d o fault d am age zones evolve? H ow d o extensional d etachm ents and thrust belt d écollem ents w ork? A m yriad of ad d itional questions could be asked about d ifferent structural processes
Tw o fund am ental reasons und erlie the gulf betw een trad itional structural g eology and geod esy, both related to the fact that m uch of the geod etic signal w e observe is related to the earthquake cycle: First, a significant part of that d eform ation is elastic
The frequency d istribution of both geod etically and geologically constrained fault slip rates in southern California suggest that 97% of the d eform ation betw een the Pacific and N orth Am erican plates is accom m od ated on faults slipping ≥ 1 m m / yr (Mead e, 2007)
Summary
Structural geologists have alw ays w anted to stud y the grow th of structures in real tim e: how d o limbs of fold s rotate? H ow d o fault d am age zones evolve? H ow d o extensional d etachm ents and thrust belt d écollem ents w ork? A m yriad of ad d itional questions could be asked about d ifferent structural processes. W e can sam ple in real tim e the surface effects of on -going structural processes via space-based geod esy. Tw o fund am ental reasons und erlie the gulf betw een trad itional structural g eology and geod esy, both related to the fact that m uch of the geod etic signal w e observe is related to the earthquake cycle: First, a significant part of that d eform ation is elastic. W e exam ine the m ost com m on analytical m ethod s cu rrently used (calculation of velocity grad ient field s and elastic block m od eling) and the issues and artifacts surround ing those method s For both of these m ethod s, questions about spatial scaling and continuo us (or d iscontinuous) n ature of surface d eform ation are key. The ad vent of space-based geod etic m easurem ents has allow ed these surveys to be d one m ore frequently, m ore d ensely, m ore precisely, and over larger areas of the w orld
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