Earthquake and Faulting, Tectonic Plate Plate Tectonic Theory Earthquake - manifestation of ground shaking caused by sudden release of energy • dislocations of crust • volcanic eruptions • man-made explosions • collapse of underground cavities (mine/karsts) - natural disturbances • fault rupture-induced • volcanic • mining-induced • large reservoir-induced • ⁃ occurrence explain by the Plate Tectonic Theory (large-scale tectonic processes) - Tectonic Plate Theory - derives from the theory of continental drift and sea floor spreading - 19th Century (Udias, 1999) - understanding between geophysics and geology began - Earthquake is recognized as a symptoms of active tectonic movement (Scholz, 1990) THE STRUCTURE OF THE EARTH 1. Crust - outer layer - thickness: 25-60km under continents and 4-6 under oceans 2. Mantle - interior below the crust - depth of 30 km to about 2900 km - consists of silicate rocks 3. Outer Core - layer surrounding the inner core - liquid layer - made up of iron and nickel - temperature similar to inner core 4. Inner Core - center and hottest part - solid and made up of iron and nickel - temperature of up to 5500 C - engine room of the earth PLATE BOUNDARIES Plates - large and stable rock slabs (thk 100km) - forming in crust or lithosphere and part of upper mantle - Lithosphere moves differentially on the underlying Asthenosphere (softer warmer layer, 400km thk, depth 50km in upper mantle) Continental Drift Theory - lithosphere divided into 15 plates (incl. Continental and Oceanic Crusts) Seismic Belts point where two plates meet TYPES OF PLATE BOUNDARIES 1. Divergent or Rift Zones - two plates separate themselves from one another - effusion of magma or lithosphere diverges from the interior - Mid-Atlantic Ridge and Pacific Ring of Fire 2. Convergent or Subduction Zones - adjacent plates converge and collide - forming a mountain range and a deep seafloor trench - Under- Thrusting Plate - subduction process carries slab like plate into dipping zone (WadiBenioff Zone) (650-700km) - Mariana Trench - North Pacific Boundaries (deep seafloor trench) - when oceanic crust tops one of the colliding plates, it sinks down the mantle TWO TYPES: Oceanic - two plates consisting of oceanic lithosphere collide. Oceanic Rock is mafic and heavy. It sinks easily and destroyed in subduction zones Continental - grinding plates consists of continental lithosphere. Lightweight rock and do not subduct 3. Transform Zones or Transcurrent Horizontal Slip - two plates glide past one another - without creating new lithosphere or subducting old - can be found on oceanic or continental lithosphere - earthquakes are common along these faults - San Andreas Fault Zone - connecting two spreading ridges (North America - Gulf of California to the South and Pacific Plates- Gorda Ridge in the North) FAULTING - Elastic Rebound - rock on one side of the fault suddenly slip with respect to the other (resulting to fracture - FAULT) - Earthquake- ground motion affected in the slip mechanism of active faults - Azimuth(∅) - angle between trace of fault (0< theta < 360) - Dip (𝛿) - between fault and horizontal plane (0<theta<90) - Slip or rake (𝜆)- between direction of relative displacement and horizontal direction (-180 < lambda < 180) - Relative Displacement (𝛥𝜇) - distance traveled by a point. Varies along fault plane - Area (S) - surface area Azimuth, Dip, and Slip or Rakes angles and its dimensions are given by its area (S) and the fault slip is measured by the relative displacement. COMMON MECHANISM OF EARTHQUAKE 1. Dip-slip Fault - move along the direction of the dip plane 1. Normal Fault - Footwall upward, hanging wall downward. Tensile forces cause shearing failure 2. Reverse Fault - Hanging wall upward, footwall downward. Compressive forces causes failure 2. Strike-slip Fault - move horizontally past one another - right-lateral or left-lateral - widespread, and many found at the boundary between obliquely converging oceanic and continental - San Andreas Fault - San Francisco earthquake of 1906 (max movement of 6m) - Anatolian Fault - Izmit earthquake of 1999 (moved more than 2.5m) - Blind Trust fault aka reverse fault - worrisome, hidden. They are folded over the tip of the fault. 3. Oblique-slip fault - normal or reverse or left or right lateral - has a component of dip slip and strike slip Earthquakes will be concentrated in the vicinity of faults. Faults that are moving more rapidly will tend to have higher rates of seismicity. Larger faults = larger events. Earthquakes continue to occur on unknown or inactive faults. PPT NI SIR Common Natural Hazards in the Ph 1. Earthquake 2. Tsunami 3. Volcanic Eruptions 4. Typhoon 5. Storm Surge 6. Flood EXAMPLES: 1. Flood in Metro Manila, Rizal and Laguna due to Tropical Cyclone Ondoy (2009) 2. Storm Surge in Eastern Visayas due to Tropical Cyclone Yolanda (2013) 3. 1991 Pinatubo Eruption and Subsequent Lahars 4. M7.8 Luzon Earthquake (July 16, 1990) - Magsaysay Bridge, Dagupan - Dagupan City - Saint Mary’s Academy, Agoo - Carmen Brudge, Rosales Earthquake - Vibratory ground motions - Totally unexpected and nearly instantaneous devastation - not designing them to resist such forces can bring serious economic consequences - - threat that earthquakes pose to life and property is not the only concern to modern societies strong earthquakes at any given location occur, on average, only once every 50–100 years Outermost Part of Earth’s interior - Asthenosphere – lies below lithosphere, low viscosity, shear strength, can flow like a liquid - Lithosphere – consists of crust and rigid uppermost part of mantle. Broke up into tectonic plates The Pacific Plate - boundary of the Pacific plate is the source of nearly half of the world’s great earthquakes - Stretching 40,000km (24,000miles) around the circumference of the Pacific Ocean (Japan, West Coast of North America, and highly populated areas – Ring of Fire) Ring of Fire - the plates that make up the Pacific basin are generally subducting beneath continental plates, causing subduction-zone volcanism at the surface - Nearly 80% of the earth’s volcanoes are found near the tectonic plate boundaries of the Pacific Ocean. - Tectonic plates move relatively slowly (5cm per year is relatively fast) and irregularly Theory of Tectonic Plates - explains the relative movement of the plates present in the Earth’s outer layer - one giant super continent – Pangaea - Pangaea - Due to the heat built up underneath the continent, it began to rift and split apart Types of Plate Boundaries 1. DIVERGENT BOUNDARIES - Plates are moving apart or away from each other. 2. CONVERGENT BOUNDARIES - Plates are colliding. 3. TRANSFORM BOUNDARIES - Plates slide past each other The lateral movement of the plates is mainly at the speeds of 50-100 mm annually. Earthquakes, volcanoes, mountain and oceanic trench formation normally occur along these boundaries. Fault - longer a fault the larger the earthquake it can generate Platelets – smaller sub plates Jostling – simple blocks of crust that occasionally move and shift 2.) the process where an oceanic plate slides beneath a continental plate is known as SUBDUCTION 3.) They travel more slowly and reach the surface after the P-waves. They transmit more energy, thus causing the bulk of damage to structures. S-WAVES 4.) They travel with a velocity that depends on the elastic properties of the rock through which they travel P-WAVES 5.) The lateral movement of the plate is mainly at the speeds of _____ mm annually 50-100 6.) A fault in which the upper block, above the fault plane, moves up and over the lower back. REVERSE FAULT 8.) The occurrences of earthquake may be explained by the theory of large-scale tectonic processes, referred to as __________ PLATE TECTONICS 9.) The portion of the Earth’s interior below the crust, extending from a depth of about 30km to about 2,900km ; it consists of dense silicate rocks. MANTLE 10.) It is characterized by rising hot mantle material and sinking colder material, forming convection currents. It is the primary driver of Plate tectonic movements. MANTLE CONVECTION 11.) The San Andreas fault of California is which type of fault? STRIKE SLIP FAULT 12.) These are large and stable rock slabs with a thickness of about 100km forming the crust or lithosphere and part of the upper mantle of the earth. PLATES 13.) What is the angle between the fault and the horizontal plane? DIP 14.) It occurs when the hanging wall moves upward in relation to the footwall, compressive force causes the failure. REVERSE FAULT 15.) Obtained when the block underlying the fault plane, or “footwall”, moves up the dip and away from the block overhanging the fault plane, or “hanging wall” NORMAL 16.) The motion of this wave is a combination of longitudinal, compressional, dilation. As result, the particles move elliptically in a vertical plane. RAYLEIGH WAVES 17.) The energy of __________ spreads from the source in two directions rather than in three. LOVE WAVES 18.) It emanates from the focus and travel in all directions through the body of the Earth. BODY WAVES 19.) The point on the Earth’s surface directly above the focus is the _________. EPICENTER 20.) It causes alternate push (compression) and pull (tension) in the rock. P-WAVES • Faulting and Seismic Zones of the Philippines WIKIPEDIA • Philippine Archipelago – geogically part of Philippine Mobile Belt (PMB) located at Philippine Sea Plate, the South China Sea Basin of the Eurasian Plate, and the Sunda Plate. • Philippine Trench (Mindanao Trench) – submarine trench (found directly east of the PMB), result of a collision • Philippine Sea Plate – subducting under PMB at the rate of about 16 cm (6.3 in) per year. • Philippine Fault System – consists of seismic faults • Galathea Depth in the Philippine Trench (at Philippine Sea) – deepest point in the Ph, 3rd deepest in the world • Philippines - Located on the western fringes of the Pacific Ring of Fire - Experiences frequent seismic and volcanic activity - Benham Plateau – east in the Philippines, an undersea region active in tectonic subduction - 20 earthquakes registered daily - 1990 Luzon Earthquake – last major earthquake - Active Volcanoes: Mayon Volcano, Mount Pinatubo, and Taal Volcano - Eruption of Mt. Pinatubo – second largest terrestrial eruption of the 20th century - World’s second-biggest geothermal energy producer behind US - 18% of the country’s energy needs ACCORDING TO NATURAL HAZARDS AND EARTH SYSTEM SCIENCES OPEN ACCESS DISCUSSIONS • Philippine Archipelago - mature island arc, accreted to the Eastern Margin of the Eurasian Plate - composed of a complex mixture of 20 terranes formed through plate interaction of the Philippine Sea Plate, Eurasian Plate, and Indo- Australian Plate - characterized by a system of subduction zones, • Philippine Mobile Belt (PMB) – actively deforming region of the Ph and bound on both 25 sides West-Dipping Subduction Zones East Luzon Trough Philippine Trench East-Dipping Subduction Zones Negros Trench Sulu Trench Cotabato Trench • • - collision zones, and wrench faults • • - Left-lateral Philippine Fault – between west and east dipping subduction zones Straddles the entire length PMB Active Faults in Bohol Cebu lineaments Central Negros Fault Panay Fault West Mindanao Fault Major Sites of Seismicity Trenches in the east and west of the archipelago ➢ South China Sea subducts along the eastdipping Manila trenches ➢ Sulu Sea subducts along the Negros trenches ➢ Celebes Sea subducts along the Cotabato trenches ➢ Sulu Trench is the locus where the Sulus Sea is consumed ➢ Philippine Trench is where the Philippine Sea Plate subducts PHILIPPINE FAULT ZONE (PFZ) • Extends 1200 km across the Philippine Archipelago • Left-lateral strike-slip fault extends NW-SE (N20 – 40W) • The fault experiences a slip rate of approximately 2-2.5 cm/yr According to the seismologists, the deepest earthquakes happen on fault lines. PHILIPPINES 5 ACTIVE FAULT LINES 1. Marikina Valley Fault - Most dangerous fault - Fault cuts through almost all the progressive and crowded portions of Manila - Two major segments: West Valley Fault and East Valley Fault - West Valley Fault – capable of producing large scale earthquakes (magnitude of 7 above) o Locations that the Marikina Valley runs through: ▪ Marikina, Montalban, San Mateo, Pasig, Taguig, Muntinlupa, San Pedro, Binan, Santa Rosa, Carmona, Tagaytay, Calamba, Oriental Mindoro 2. Western Philippine Fault - Runs in the waters of the western part of the PH o Places where the fault line passes: ▪ Mindoro Strait, Luzon Sea, Sulu Sea, Panay Gulf 3. East Philippine Fault - Found beneath the ground - Found at the Philippine Sea 4. Southern of Mindanao Fault - Runs through the Celebes Sea as well as the Moro Gulf 5. Central Philippine Fault - Runs through several provinces in cities from northern part of archipelago to southern part of Davao o Places where the fault line passes: ▪ The entire Ilocos Norte, Aurora, Quezon, Masbate, Eastern Leyte, Southern Leyte, Agusan Del Norte, Agusan del Sur, Davao del Norte - Root of the earthquake which destroyed the Guinsaugon, Baguio and the Central Luzon part in 1990 4. The 1994 Mindoro Earthquake Magnitude: 7.1 Description - November 15 - Maximum intensity of VII (Very Strong) - 35 km long ground rupture (Aglubang River Fault) Results - Total of 1530 houses in the coastal areas of Bacoand Calapan, Oriental Mindoro were swept away by a tsunami generated by the earthquake - Killed 78 people LARGEST EARTHQUAKE IN PH SINCE 1960s 1. The 1968 Casiguran Earthquake Magnitude: 7.3 Description - August 2 - Moment magnitude 7.6 - Max intensity of IX (9) - Epicenter was in Casiguran, Quezon (now Aurora Province) Results - Killed 270 people - Caused massive landslide and tsunami - Almost 300 people killed when the Ruby Tower in Binondo collapse 5. The 2013 Bohol Earthquake Magnitude: 7.0 Description - October 15 - Epicenter 6 km S24W of Sagbayan - Depth of focus was 12 km - Affected the whole central Visayas Region (Bohol and Cebu) Results - NDRRMC – 222 dead, 8 missing, 976 injured - More than 73,000 structures damaged - More than 14,500 totally destroyed - Deadliest earthquake in the PH after 23 years since 1990 Luzon Earthquake 2. The 1976 Moro Gulf Earthquake Magnitude: 8.0 Description - A tsunami also took place on August 17 near the islands of Mindanao and Sulu - Highest magnitude calculated Results - 3000 casualties - Officially the strongest and deadliest earthquake in Ph history - Almost 40,000 people in Regions 9 and 12 were left homeless 3. The 1990 Luzon Earthquake Magnitude: 7.8 Description - Maximum intensity of IX (Violent) - Produced a 125 km-long ground rupture (Dingalan, Aurora to Cuyapo, Nueva Ecija) - Strike-slip movements Results - Total of 1,621 deaths - Serious damage of properties
