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2.2 active faults & other earthquakes source zones

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2.2 active faults & other earthquakes source zones

  1. 1. Active Faults & OtherActive Faults & Other Earthquake Source ZonesEarthquake Source Zones Mariton V. BornasMariton V. Bornas Geology & Geophysics R&D DivisionGeology & Geophysics R&D Division Philippine Institute of Volcanology & SeismologyPhilippine Institute of Volcanology & Seismology
  2. 2. ACTIVE FAULTS
  3. 3. •FAULTING is the cause of TECTONIC EARTHQUAKES. •3 types of faults are called NORMAL, THRUST or REVERSE and STRIKE-SLIP. FAULT: a fracture, fissure, or a zone of weakness where ground movement or displacement has occurred or may occur again. WHAT IS A FAULT?
  4. 4. BEFORE FAULTING REVERSE NORMAL FAULT STRIKE-SLIP BEFORE FAULTING REVERSE NORMAL FAULT STRIKE-SLIP TYPES OF FAULT
  5. 5. Normal FaultNormal Fault
  6. 6. Thrust or Reverse FaultThrust or Reverse Fault
  7. 7. Thrust fault of the 1999 Chichi Earthquake, TaiwanThrust fault of the 1999 Chichi Earthquake, Taiwan
  8. 8. Thrust fault of the 1999 Chichi Earthquake, TaiwanThrust fault of the 1999 Chichi Earthquake, Taiwan
  9. 9. StrikeStrike--slip Faultslip Fault
  10. 10. Nojima Fault of the 1995 HanshinNojima Fault of the 1995 Hanshin--Awaji (Kobe) Earthquake, JapanAwaji (Kobe) Earthquake, Japan
  11. 11. LeftLeft--laterally displaced pilapils (rice paddy dikes) in Imugan, Nuevalaterally displaced pilapils (rice paddy dikes) in Imugan, Nueva VizcayaVizcaya along the Digdig Fault rupture of the 1990 Northern Luzon Earthqalong the Digdig Fault rupture of the 1990 Northern Luzon Earthquake.uake.
  12. 12. ““Mole tracksMole tracks”” defining the Digdig Fault rupture afterdefining the Digdig Fault rupture after the 1990 Northern Luzon Earthquake.the 1990 Northern Luzon Earthquake.
  13. 13. Aerial view of the San Andreas FaultAerial view of the San Andreas Fault System, the most famous strikeSystem, the most famous strike--slipslip fault in the world. The San Andreasfault in the world. The San Andreas Fault marks the boundary betweenFault marks the boundary between the Pacific Sea Plate and the Norththe Pacific Sea Plate and the North American PlateAmerican Plate
  14. 14. A fault is defined as an ACTIVE FAULT when it has moved within the last 10,000 years (Holocene Period). WHAT IS AN ACTIVE FAULT? BASES OF MOVEMENT: 1. historical and contemporary seismicity (earthquake activity) 2. fault slip (displacement) based on displaced rock or soil units of known age (paleoseismology) 3. displaced landforms (active fault geomorphology)
  15. 15. Active Faults & Trenches Philippine seismicity from 1600s to present
  16. 16. DOST PHIVOLCS
  17. 17. B: Triangular facet H: Offset stream C: Fault sarplet I: Shutter ridge D: Sag pond J: Beheaded stream E: Pressure ridge K: Wind gap F: Fault saddle L: Offset piedmont line G: Graben M: Offset alluvial terrace Smith & Wesson, 1975) Active StrikeActive Strike--slip Fault Geomorphologyslip Fault Geomorphology
  18. 18. Pressure ridges bench offset streams sagpond Gabaldon Fault Gabaldon Fault Digdig Fault 1990 rupture Digdig Fault 1990 rupture Sample airphoto interpretation of the Gabaldon Fault, Dingalan, Aurora
  19. 19. A weak to violent shaking of the ground produced by the sudden movement of rock materials below the earth’s surface (FAULTING). WHAT IS AN EARTHQUAKE
  20. 20. •based on relative ground shaking effect to people and structures; generally higher near the epicenter •(Reported in Roman Numerals e.g. I, II..IV..IX) •based on instrumentally derived data; measure of the amount of total energy released at the earthquake’s point of origin •(Reported in Arabic numerals e.g. 3.5, 7.2, etc) 1. Intensity 2. Magnitude Two Earthquake Descriptions:Two Earthquake Descriptions:
  21. 21. ACTIVE FAULTS & OTHER EARTHQUAKE GENERATORS OF THE PHILIPPINES
  22. 22. Most Destructive Earthquakes in the Philippines
  23. 23. Recent Destructive Earthquakes • 1968 Casiguran – Ms 7.3 • 1973 Ragay Gulf – Ms 7.0 • 1976 Moro Gulf – Ms 7.9 • 1983 Laoag – Ms 6.5 • 1990 Luzon – Ms 7.8 • 1990 Bohol – Ms 6.8 • 1990 Panay – Ms 7.1 • 1994 Mindoro – Ms 7.1 • 2002 Sultan Kudarat – Ms 6.8 • 2003 Masbate – Ms 6.2
  24. 24. Earthquake Generators in the Philippines
  25. 25. Earthquake Generators in the Philippines
  26. 26. PHILIPPINE FAULT ZONE: •1,300 km-long fault system that stretches N-S from Ilocos to eastern Mindanao •Left-laeral strike-slip •Average slip rate: 1.5 to 3.6 cms/year •M7.8 July 16, 1990 Luzon Earthquake along the Digdig Fault segment, the M7.3 March 17, 1970 Ragay Gulf Earthquake, and the M6.2 February 15, 2003 Masbate Earthquake ACTIVE FAULTS IN THE PHILIPPINES
  27. 27. VALLEY FAULT SYSTEM (VFS): •Originally the Marikina Fault, a pair of segmented faults that forms the Marikina River Valley and transects the eastern margins of Metro Manila •Consists of the West Valley Fault (WVF) and the East Valley Fault (EVF) •Right-lateral strike-slip fault. ACTIVE FAULTS IN THE PHILIPPINES
  28. 28. Trenches as Earthquake Generators
  29. 29. The Philippine Trench Zone where the Philippine Sea Plate (PSP) subducts beneath the Philippine Mobile Belt (PMB) between offshore Bicol Peninsula and southeast Mindanao. Convergence between the PSP and the PMB occurs at the rate of 8 cms/year East Luzon Trough Zone where the PSP subducts beneath the PMB offshore of northeastern Luzon. The Manila Trench Zone where the South China Sea Plate (SCSP) subducts beneath the PMB between Taiwan and Mindoro. PHILIPPINE SUBDUCTION ZONES
  30. 30. Negros Trench Zone where the Sulu Sea Plate (SSP) subducts beneath the PMB offshore of Panay and Negros Island. Sulu Trench Zone where the SSP subducts beneath the PMB offshore of Zamboanga Peninsula and Sulu Archipelago. Cotabato Trench Zone where the Celebes Sea Plate subducts beneath the PMB offshore of the Cotabato and Saranggani Provinces. PHILIPPINE SUBDUCTION ZONES
  31. 31. Metro Manila and the VALLEY FAULT SYSTEM (VFS)
  32. 32. Surface Geology of Metro Manila East Valley Fault West Valley Fault
  33. 33. Source: HIGP, Univ. Hawaii West Valley Fault Manila Bay
  34. 34. The Worst Case Scenario Earthquakes Model M Characteristi cs08 – West Valley Fault 7. 2 Severe Damage 13 – Manila Trench 7. 9 Tsunami West Valley Fault Manila Trench Worst-case Scenario Earthquakes for Metro Manila
  35. 35. THANK YOU FOR YOUR ATTENTION☺☺☺☺

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