A Passive Plate Margin Continental Margins Are Not Necessarily Plate Margins! Earthquake Locations

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A passive plate margin Continental margins are not necessarily plate margins! Earthquake Locations Geologists define three types of plate boundary, based simply on the relative motions of the plates on either side of the boundary. These basic types– divergent, convergent, and transform plate boundaries–are shown in this three-part animation. PC version Mac version Cascades volcanic arc (NW US) Mid-Atlantic Ridge as seen in Iceland San Andreas fault Zoomable Art PC Mac Geologists define three types of plate boundary, based simply on the relative motions of the plates on either side of the boundary. These basic types– divergent, convergent, and transform plate boundaries–are shown in this three-part animation. PC version Mac version This animation shows the development of a transform fault along a divergent plate boundary. Plates slide past one another along a transform fault without the formation of new plate or the consumption of old plate. As this process occurs, new sea floor forms along the mid ocean ridge. PC version Mac version Rifting is the process by which a continent splits and separates to form a new divergent boundary. This animation shows the progressive formation and evolution of a continental rift, and the formation of a mid-ocean ridge. PC version Mac version At convergent plate boundaries or convergent margins, two plates, at least one of which is oceanic, move toward each other. But rather than butting each other like angry rams, one oceanic plate bends and begins to sink down into the asthenosphere beneath the other plate. This sinking process, termed subduction, is shown in the following animation. PC version Mac version .

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Transform Faults Represent One of the Three
8 Transform faults ransform faults represent one of the three Because of the drift of the newly formed oceanic types of plate boundaries. A peculiar aspect crust away from ridge segments, a relative move- T of their nature is that they are abruptly trans- ment along the faults is induced that corresponds formed into another kind of plate boundary at their to the spreading velocity on both sides of the termination (Wilson, 1965). Plates glide along the ridge. Th e sense of displacement is contrary to fault and move past each other without destruc- the apparent displacement of the ridge segments tion of or creation of new crust. Although crust is (Fig. 8.1b). In the example shown, the transform neither created or destroyed, the transform margin fault is a right-lateral strike-slip fault; if an observer is commonly marked by topographic features like straddles the fault, the right-hand side of the fault scarps, trenches or ridges. moves towards the observer, regardless of which Transform faults occur as several diff erent geo- way is faced. Transform faults end abruptly in a metries; they can connect two segments of growing point, the transformation point, where the strike- plate boundaries (R-R transform fault), one growing slip movement is transformed into a diverging or and one subducting plate boundary (R-T transform converging movement. Th is property gives this fault) or two subducting plate boundaries (T-T fault its name. In the example of the R-R transform transform fault); R stands for mid-ocean ridge, T for fault, the movement at both ends of the fault is deep sea trench ( subduction zone).
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Segmentation of Transform Systems on the East Pacific Rise
Segmentation of transform systems on the East Paci®c Rise: Implications for earthquake processes at fast-slipping oceanic transform faults Patricia M. Gregg Massachusetts Institute of Technology/WHOI Joint Program in Oceanography, Woods Hole, Massachusetts 02543, USA Jian Lin Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA Deborah K. Smith ABSTRACT Per®t et al., 1996) indicate that ITSCs are Seven of the eight transform systems along the equatorial East Paci®c Rise from 128 N magmatically active, implying that the regions to 158 S have undergone extension due to reorientation of plate motions and have been beneath them are hotter, and thus the litho- segmented into two or more strike-slip fault strands offset by intratransform spreading spheric plate is thinner than the surrounding centers (ITSCs). Earthquakes recorded along these transform systems both teleseismically domains. To explore the effect of segmenta- and hydroacoustically suggest that segmentation geometry plays an important role in how tion on the transform fault thermal structure, slip is accommodated at oceanic transforms. Results of thermal calculations suggest that we use a half-space steady-state lithospheric the thickness of the brittle layer of a segmented transform fault could be signi®cantly cooling model (McKenzie, 1969; Abercrom- reduced by the thermal effect of ITSCs. Consequently, the potential rupture area, and bie and Ekstrom, 2001). The temperature thus maximum seismic moment, is decreased. Using Coulomb static stress models, we within the crust and mantle, T, is de®ned as T 5 k 21/2 illustrate that long ITSCs will prohibit static stress interaction between transform seg- Tmerf [y(2 t) ], where Tm is the mantle ments and limit the maximum possible magnitude of earthquakes on a given transform temperature at depth, assumed to be 1300 8C; k system.
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Transform Continental Margins – Part 1: Concepts and Models Christophe Basile
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Two Classes of Transform Faults
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Origin and Models of Oceanic Transform Faults
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On the Thermal Structure of Oceanic Transform Faults 2 Mark D
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Chapter 10: Earth Hazards of the weather • the measure Western US of short-term conditions of the atmosphere such as temperature, wind speed, and Natural hazards are events that result from natural processes and that humidity. have signifi cant impacts on human beings. Extreme weather conditions or geologic activity can cause substantial short-term or long-term changes to our environment. These changes can infl uence crops, homes, infrastructure, and plates • large, rigid pieces of the atmosphere. The 4.6-billion-year-old Earth has experienced many of these the Earth’s crust and upper natural changes, and it has always adjusted accordingly. mantle, which move and interact with one another at their boundaries. The Western United States is located at the junction of three tectonic plates: the Pacifi c, the Juan de Fuca, and the North American. The movement of these plates, even though it occurs on the scale of millimeters per year, makes the Western US a dynamic landscape. The dramatic result is a dizzying assortment subduction • the process of natural hazards such as earthquakes, tsunamis, landslides, and volcanoes. by which one plate moves The Pacifi c plate is subducting under Alaska, creating the volcanoes of the under another, sinking into the mantle. Aleutian Islands. The Juan de Fuca plate is subducting under Washington, Oregon, and Northern California, creating the Cascade volcanoes, and the Pacifi c plate is grinding past the North American plate along the famous San Andreas Fault. At the same time, the Basin and Range province, which includes fault • a fracture in the Earth’s nearly the entire state of Nevada, is being stretched and faulted by plate crust in which the rock on one side of the fracture moves movement.
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On the Segmentation of the Cephalonia–Lefkada Transform Fault Zone (Greece) from an Insar Multi-Mode Dataset of the Lefkada 2015 Sequence
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