An Introduction to Structural Geology and Tectonics
When people hear that you are studying to be a geologist, one of the first questions you'll be asked in North America is, "Will California fall into the ocean?" Perhaps the legend of the vanishing state originated from the observed huge slumps forming along the Pacific coast during large earthquakes. Most of the tremors jolting California are due to sudden increments of movement along the San Andreas fault, which is an example of a major continental strike-slip fault zone. Across the fault zone, the Pacific plate moves north, relative to North America. Other impressive examples of continental strike slip zones include the Alpine fault in New Zealand, the Anatolian faults in Turkey, the Chaman fault in Pakistan, and the Red River and Altyn Tach faults of China. Strike-slip faults also cut oceanic lithosphere, in particular along ocean ridges, but because oceanic strike-slip fault zones are hidden by the sea, they are not as well known as their continental kin. Maybe, when reading about strike-slip faulting, you've come across some of these terms: wrench, tear, transfer, lateral ramp, transcurrent, and transform. Unfortunately, different authors use strike-slip fault terminology in different ways, leading to some confusion about their meaning. In this chapter we examine these and related concepts.
In the previous chapters, we already mentioned strike-slip faults on several occasions, because they occur as components of contractional and extensional tectonic regimes. In this chapter, we focus on these faults themselves. Specifically, we examine the structure and kinematics of various types of strike-slip faults (both oceanic and continental), the geometry of the subsidiary structures that form in association with these faults, and the tectonic settings in which they occur. We begin by clarifying the distinction between the two kinematic classes: transfer and transcurrent faults.