Plate tectonic activity with maps
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  • Add JOI and ODP logos, and Rice logo. And thanks for JOI,USSSP, etc.
  • The fourth, and perhaps the richest of the data maps, shows the topography and bathymetry of the Earth. This is the elevation of the land surface and the depth of the oceans. The map uses color to indicate varying elevation and depth and simulates sun shading to add a sense of 3-dimensionality to the map. The scale bar on the right shows how colors on the map correspond to elevation in meters.
  • An exercise based on observing, describing, and classifying data must be built on some rich and well displayed data. I use 4 data maps that contain an amazing amount of information about large scale plate tectonic processes on the Earth. These data have been acquired over many years by many scientists. When examined together, most of the basic tenets of plate tectonics are laid bare and seem irrefutable. Scientists developing the key ideas of plate tectonics over the past 40 years had only fragments of these data to work with as they tried to describe, classify, and interpret what they saw. In Discovering Plate Boundaries, you will be asking your students to walk the same path, but with the advantage of more complete, although not perfect, data. The first map shows earthquake locations and depths. The location of each earthquake is indicated by a small dot and its depth is indicated by the color of the dot. Red dots indicate earthquakes having depths between zero and 33 km. We refer to these as shallow earthquakes. The yellow or orange dots indicate earthquakes having depths between 33 and 70 km. We call these intermediate depth earthquakes. The green dots indicate earthquakes having depths between 70 and 300 km We call these deep earthquakes. The blue dots indicate earthquakes having depths between 300 and 700 km. We call these ultra-deep earthquakes.
  • The second map shows the locations of recent volcanic or thermal features on the Earth. In this dataset, recent refers to the past 10,000 years. The dots represent volcanoes, geysers, hot springs, and similar features. In these slides, the maps are not shown in a way that you can see all the detail. The second part of the Teachers Guide, called A Tour of the Maps, shows the maps in much more detail. It is also possible to download the maps in several high resolution formats from the DPB website so that you can see the details.
  • The third map shows the age of the oceanic crust under most of the world’s oceans. This map really highlights divergent plate boundaries, also known as mid-ocean ridges or spreading centers. The scale bar on the right shows how the colors correspond to age of the seafloor in millions of years. Red signifies the youngest crust. Blue signifies the oldest known oceanic crust. An important feature of the maps used in this exercise is that they are all displayed at the same scale and projection, and use the same coastline data. Uniformity of the map base makes it easy for students to compare data from map to map. This is an important aspect of the exercise. It is possible to obtain excellent maps (better than mine!) of each of these data from other sources, but they are unlikely to be displayed in the same way. I have found inconsistent display to be a source of frustration for students.
  • The fourth, and perhaps the richest of the data maps, shows the topography and bathymetry of the Earth. This is the elevation of the land surface and the depth of the oceans. The map uses color to indicate varying elevation and depth and simulates sun shading to add a sense of 3-dimensionality to the map. The scale bar on the right shows how colors on the map correspond to elevation in meters.
  • When the students arrive for the first period of the class, I hand out the Student Instruction sheet, and a plate boundary map. I use 11 by 17 in black and white maps that I make on a copying machine. They are displayed at the same projection and base as the data maps, although to a smaller scale. I also hand each student a slip of paper with a Scientific specialty (Seismology, Geochronology, Volcanology, or Geography) and a Plate Name (Pacific Plate, North American Plate, African Plate, and etc.). My goal is to have each student have a different combination of specialty and plate, and for all four scientific specialties to be covered for each plate used in the exercise. Therefore, if you have 24 students, I would use 6 plates and have all four specialties for each. Numbers that are not multiples of four can be handled by having 1-3 plates with only 3 specialties. If I have to do this, I drop a different specialty from each, but never Seismology. I bet you can guess that I am a Seismologist! I mix the specialties and plates up randomly among students because I think this exercise works best if they are not self arranged into their usual social groupings.
  • The fourth, and perhaps the richest of the data maps, shows the topography and bathymetry of the Earth. This is the elevation of the land surface and the depth of the oceans. The map uses color to indicate varying elevation and depth and simulates sun shading to add a sense of 3-dimensionality to the map. The scale bar on the right shows how colors on the map correspond to elevation in meters.

Plate tectonic activity with maps Plate tectonic activity with maps Presentation Transcript

  • Earthquakes in the Ocean: Where, Why, and What Happens? As prepared for ESCI 323 - Earth Structure & Deformation And Sally Ride Festival , Houston (10/25/06) Prof. Julia Morgan Dr. Meghan Miller Department of Earth Science Rice University
  • Dale Sawyer’s Discovering Plate Boundaries Exercise (http://terra.rice.edu/plateboundary)
    • Designed for students to observe & classify
    • Appropriate for broad range of ages/exper.
    • Designed for 3 days, w/ variations
    • Excellent framework for MARGINS & similar
    An aside:
  • Seismology Map – Earthquake Locations and Depths
  • Volcanology Map – Recent Volcanic Activity
  • Geochronology Map – Seafloor Age
  • Geography Map – Topography and Bathymetry
  • Plate Boundary Map
  • Where do all the earthquakes occur?? (Press et al., Understanding Earth, 4th Ed.)
  • Kurile Earthquake Nov. 15, 2006 Juli
  • Tectonic Setting - Kuriles
    • Subduction of Pacific Plate Plate beneath Okhotsk/N. America.
    • Conv. rate: ~ 9 cm/yr.
    • Sakhalin Island & Japan are rifted cont.
    Political Setting
    • Russia “stole” from Japan after WW II
  • Kurile Earthquake Nov. 15, 2006
  • Kurile Tsunami - Nov. 15, 2006
  • Convergent Boundaries: Three Types
    • Ocean-ocean
    • Sumatra earthquake!
    • M ~9.3 (2004)
    Ocean-continent Chile earthquake! M ~9.5 (1960) Continent-continent South Asian earthquake! M ~7.5 (2005) In the Oceans (Press et al., Understanding Earth, 4th Ed.)
    • M 9.5 Earthquake (Largest worldwide)
    • Rupture zone ~1000 mi long.
    • Generated a tsunami that spread across Pacific.
    • Run-up: 25 m in Chile; 10.7 in Hilo; 1.7 in CA.
    • ~ 6000 people died, most from tsunami.
    • $3.5 Billion property damage
    Chile - 5/22/1960 (Source: Sawyer, Discovering Plate Boundaries)
    • M 9.2 Earthquake (3rd or 4th largest worldwide)
    • 750 mi long rupture zone.
    • Large landslide and tsunami across Pacific.
    • Ground displacements 25 ft x 3 ft.
    • 122 people died worldwide, most from tsunami.
    • Property damage $500 million.
    Alaska - 3/27/1964 (Source: Sawyer, Discovering Plate Boundaries)
  • Alaska Tsunami (Press et al., Understanding Earth, 4th Ed.)
    • M 9.3 Earthquake (2nd largest worldwide)
    • 1000 km long fault rupture.
    • Generated a tsunami that went around the world.
    • No warning.
    • More than 200,000 people died.
    • Untold property damage….
    Southeast Asia - 12/26/2004 (Source: Sawyer, Discovering Plate Boundaries)
  • Sumatra Earthquake Fault zone rupture ~ 1000 km in length Epicenter Sumatra Indian Plate (Source: USGS)
  • What is a tsunami & How does it form?
    • A sudden impulse pushes the water, forming a train of waves that spreads outward from the source.
    • Tsunami front propagates at ~450 mi/hr (~600 km/hr).
    (Source: Prof. Miho Aoki, U. Alaska Fairbanks)
  • Tsunami Generation & Propagation
    • Sumatra Tsunami (12/26/04)
    • red: rise in sea level
    • blue: fall in sea level
    (http://staff.aist.go.jp/kenji.satake/animation.gif)
  • What Happens Nearshore?
    • As the water column shallows, wave height grows.
    • Tsunami run-ups can be MUCH larger than original wave.
    (Press et al., Understanding Earth, 4th Ed.)
  • What are the Consequences?
    • Coastal damage and destruction.
    (Source: Prof. Miho Aoki, U. Alaska Fairbanks)
  • Can This Happen in N. America? Yes!!
    • M ~9 Cascadia Earthquake (7th largest?)
    • No historic record in North America.
    • Recorded in Japan ~9 hrs later.
    • Tsunami deposits found along Oregon coast.
    • Recurrence interval is 300-500 yrs!
    Oregon-Washington - 1/26/1700 (Source: Sawyer, Discovering Plate Boundaries)
  • January 1700 Cascadia Tsunami (Source: K. Satake, http://www.pgc.nrcan.gc.ca/press/index_e.php)
  • Where do Great Earthquakes occur? Seismogenic Zone Coseismic Slip Aseismic Slip Tsunamigenic Slip
    • Plate boundary mega-thrust
    Sediments Rocks Why do Great Earthquakes occur?
  • Where can we study great earthquakes?
    • Nankai Trough
    • Subduction of the Philippine Sea Plate beneath Eurasia.
    • Convergence rate: ~4 cm/yr.
    • Thick clastic-rich sediment section (hemipelagites and turbidites).
  • Earthquake Recurrence
    • Nankai margin is subject to repeated large (M ~ 8) earthquakes.
    • Evidence for tectonic segmentation of the margin.
    • Earthquake recurrence ~180 yrs.
    • -> There will be future earthquakes!!
    (Ando, 1975)
  • Co-seismic Slip Zone (Bangs et al., 2004) Up-dip limit
  • Recent Ocean Drilling & Surveys
  • Toe of Muroto Transect Decollement 1 km Proto-decollement Deformation front Proto- thrusts Frontal thrusts NANKAI TROUGH NANKAI PRISM PROTO-THRUST ZONE Depth (m) Trench Fill turbidites Shikoku Basin Strata hemipelagic sediments Ocean Crust
  • Prism Architecture (J.C. Moore and Saffer, 2001)
    • Décollement partitions the incoming section:
      • - Accreted section vs. underthrust section.
    • Décollement steps down near the updip limit.
    Seismogenic Zone Coseismic Zone Aseismic Zone (after G.F. Moore et al., 2001) Up-dip limit
  • Décollement Amplitude (Bangs et al., 2004)
    • Downdip decrease in décollement amplitude.
    • Suggests dewatering of underthrust section.
  • Pore Fluid Pressures (J.C. Moore and Saffer, 2001)
    • Modeled pore fluid pressures are highest near up-dip limit.
    (after G.F. Moore et al., 2001) Seismogenic Zone Coseismic Zone Updip limit
  • Seismic-Aseismic Transition -> Onset of Earthquakes
    • Coincident with onset of coseismic sliding:
      • Out of sequence thrust.
      • Step down in décollement.
      • Reduced décollement amplitude.
      • Increased pore fluid pressures.
    • Why? Something changes along décollement:
      • Frictional behavior: stable vs. unstable?
      • Loss of strength in underthrust sediments?
      • Something completely different?
    Future fault zone drilling may tell us….