ÖNCEL AKADEMİ: INTRODUCTION TO GEOPHYSICS

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Gravity and Isostasy

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ÖNCEL AKADEMİ: INTRODUCTION TO GEOPHYSICS

  1. 1. Ali Oncel [email_address] Department of Earth Sciences KFUPM Gravity and Isostasy Introduction to Geophysics Introduction to Geophysics-KFUPM
  2. 2. Previous Lecture <ul><li>Gravity Units </li></ul><ul><ul><li>Example 1: Mars's twin moons </li></ul></ul><ul><ul><li>Example 2:  The Valley and Ridge Province (1-5 mgals) </li></ul></ul><ul><li>Sensitivity: Density Distribution </li></ul><ul><ul><li>Sensitive to changes in Mass (Density) changes </li></ul></ul><ul><li>Densities of Geological Materials </li></ul><ul><li>On-Line Gravity Map Construction Tool </li></ul><ul><li>Color table for standard Gravity map </li></ul><ul><ul><li>Example 1: North Anatolian Fault Zone in the sea of Marmara </li></ul></ul><ul><ul><li>Example 2: Ghawar region of Saudi Arabia </li></ul></ul>Introduction to Geophysics-KFUPM
  3. 3. Parks and Plates,pp.27 ©2005 Robert J. Lillie Introduction to Geophysics-KFUPM
  4. 4. Parks and Plates ©2005 Robert J. Lillie
  5. 5. Parks and Plates ©2005 Robert J. Lillie Introduction to Geophysics-KFUPM
  6. 6. http://www.moorlandschool.co.uk/earth/tectonic.htm Introduction to Geophysics-KFUPM
  7. 7. Parks and Plates ©2005 Robert J. Lillie Topography of the Ocean Floor Introduction to Geophysics-KFUPM ©1977, Marie Thorpe
  8. 8. National Aeronautics and Space Administration Two Forms of Isostatic Uplift pp.28 Parks and Plates ©2005 Robert J. Lillie Introduction to Geophysics-KFUPM Low density due to higher temperature
  9. 9. http://www.moorlandschool.co.uk/earth/tectonic.htm Two Forms of Isostatic Uplift Introduction to Geophysics-KFUPM
  10. 10. What is Isostatic Equilibrium? <ul><li>Crust floats on Mantle </li></ul><ul><li>(hydrodynamic equilibrium) </li></ul><ul><li>Surface elevation is function of </li></ul><ul><li>underlying mass (thickness and density of crust) </li></ul><ul><li>Surface elevation is compensated by mass below it </li></ul>Introduction to Geophysics-KFUPM
  11. 11. Bouguer Anomaly <ul><li>Slightly positive over oceans </li></ul><ul><li>Slightly negative over continents </li></ul>Why? <ul><li>Because a uniform density was used in International Gravity Formula </li></ul>Introduction to Geophysics-KFUPM 2.67 g/cm 3 3.3 g/cm 3 Mantle http://www.moorlandschool.co.uk/earth/tectonic.htm
  12. 12. Example from Arabia Introduction to Geophysics-KFUPM
  13. 13. Example from Arabia Data Source: Cornell University <ul><li>Bouguer anomalies that are negative over high areas and positive over oceans. </li></ul><ul><li>Near sea level, the average is close to zero. </li></ul><ul><li>The negative Bouguer anomalies areas due to the excess of low density material at depth in mountainous regions when compared to rocks at depth in areas of low relief near sea level. </li></ul>Introduction to Geophysics-KFUPM
  14. 14. Homework, Due to May 17 <ul><li>Use the online tool for making a gravity map from the site http://www.itismolinari.mi.it/Gravity.htm . </li></ul><ul><li>Make your gravity map and compare changes in the gravity to changes through regions of major tectonics? What is the gravity through the areas: </li></ul><ul><li>a) Red Sea b) Dead Sea Fault c) Iranian Sea d) Gulf of Aqaba e) Zagros Thrust Fold </li></ul>Introduction to Geophysics-KFUPM
  15. 15. The quiz of the week For the following equation, define the variables: FAA= g obs – g th +FAC BA = FAA – BC + TC Introduction to Geophysics-KFUPM

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