GEOL 106 Lecture Notes - Lecture 6: Convergent Boundary, Plate Tectonics
15 May 2018
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3.1 Introduction to Earthquakes
- movement of tectonic plates results in formation and destruction of ocean basins, uplift of mountains
→ most active along boundaries of lithospheric plates where faulting occurs
FAULTS AND FAULTING
- fault: plane of weakness i Earth’s rust here a fault ours, oo alog plate oudaries
o semiplanar fracture or fracture system where rocks have been displaced → Earth’s urst o
one side of fracture or fracture system has moved relative to other side
- footwall: block below the fault plane where a miner would stand
- hanging wall: block above fault plane where a lantern could be hung
- friction along boundary between plates may temporarily slow their motion but rough edges break off
and motion occurs at various places along plane
- one lithospheric plate moving past another is slowed by friction along fault plane that separates plates
→ stresses rocks along fault and rocks under go strain/ deformation
- stress = force that results from plate tectonic movements
- strain = change in shape or location of rocks due to applied stress
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- three types of plate boundaries → three different types of stress: tensional, compressional, shearing,
and three primary types of faults
FAULT TYPES
- by direction in which rocks on either side are displaced
1. dip slip fault: offsets rocks in vertical motion due to compressional or tensional stresses
2. strike slip fault: offsets blocks of crust in horizontal direction due to shearing stress
- normal fault: type of fault identified by downward movement of hanging wall relative to footwall
o aused tesioal stress hih results i etesio ad thiig of Earth’s surfae tpial of
divergent plate boundaries
- reverse fault: upward relative movement of hanging wall due to compression which results in
shortening and thickenig of Earth’s surfae tpial of oerget plate oudaries
o
- strike flip fault: close to vertical and therefore does not have a hanging wall or footwall
o two different types of strike slip fault due to reversal in orientation of stresses on either side
of fault
o either right lateral or left lateral
- blind faults: do not extend to surface, do not offset rocks at surface, can identify folds at surface
known as anticlines and synclines
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