CE 107 Geology for Civil Engineers Notes PDF

CE 107: Geology for Civil Engineers Ateneo de Zamboanga University College of Science, Information Technology, and Engineering ENGR. NEIL T. BERNARDO...

CE 107: Geology for Civil Engineers Ateneo de Zamboanga University College of Science, Information Technology, and Engineering ENGR. NEIL T. BERNARDO Course Instructor The Surface of the Earth Earth’s Radius: 6370 km (Equator) 6348 km (Polar) Surface Area: 𝟓𝟏𝟎𝒙𝟏𝟎𝟔 km² (29% land or 35% including shallow sea areas) The Surface of the Earth Average Height of Land ASL: 0.86 km Mean Depth of Ocean Floor: 3.8 km Highest Peak: 8.9 km Greatest Known Depth: 11.04 km The Earth’s Spheres Geosphere Hydrosphere Atmosphere Biosphere Earth’s Interior Temperature increases by 30°c per km depth. Rocks begin to melt at approximately 30km deep. Crust Crust made of light materials while the core is made up of denser materials. The crust is broken into many pieces called plates. Mantle It is the largest layer of the Earth, 1800 miles thick. This layer of rock even flows like asphalt under a heavy weight. Outer Core Comparable to a hot ball of metals. Made of melted metals nickel and iron. Inner Core High temperatures and pressures cause the melted metals to stay intact. Earthquakes The numerous shocks which continually take place are due to sharp movements along fractures (called faults)which relieve stress in the crustal rocks. Earthquakes A small movement on a fault can already create huge shocks/effects. Young deposits of sand, silt and clay receive more damage. Lives and property may be saved if earthquake resisting structures are built Earthquakes Prior to a major earthquake, strain in the crust accumulates to the extent that small changes may be noticed. When a major earthquake at sea rapidly changes the elevation of the ocean floor, this leads to tsunamis. Earthquakes Most of the active earthquake centres at the present day are located along two belts at the Earth's surface – Circum-Pacific Belt and Alpide Belt. Earthquakes Earthquakes Earthquakes Earthquakes are commonly measured by: Intensity – Mercalli Scale Magnitude – Richter Scale Earthquakes Seismic waves are created which has two types: Body waves – composed of P-waves (fastest) and S-waves (slower) Surface waves – composed of Love waves and Rayleigh Wave Continental drift The possible movement of the continents relative to one another in the geological past was first outlined at length by Alfred Wegener in 1912. He postulated a supercontinent to which he gave the name Pangaea. Continental drift Evidence includes age of oceanic floors, similarity in geological features, fossil faunas, and continental shapes. Continental drift Continental drift Oceanic Ridges Resemble submerged mountain ranges and are found in all the oceans. The ridge extends from Iceland southwards through the North Atlantic, and thence continues into the South Atlantic about midway between Africa and South America. Oceanic Ridges After passing Tristan da Cunha the oceanic ridge turns east and continues into the Indian Ocean. Other ridges lie below the East Pacific, and between Australia and Antarctica; In the Indian Ocean a ridge runs northwards to the Red Sea. Oceanic Ridges Oceanic Ridges Along the line of its summit a deep cleft called the median rift extends to a depth of over 450 m (900 fathoms) Oceanic Ridges The North American and Eurasian Plates are moving away from each other along the line of the Mid Atlantic Ridge. Oceanic Ridges Rock samples taken in the vicinity of this rift are mainly volcanic rocks such as basalt. These materials rises along median rift and pushed aside, forming new ocean floor; ocean floor spreading – proven by rock magnetism. Rock Magnetism Samples of basaltic rocks from the North Atlantic floor increase in age with distance from the median rift; those near it are only 13 000 years old, while rocks 64 km to the west of it are about 8 million years old. The present rate of spreading is between 1 cm and 3 cm per year, though it may have varied in the past. Rock Magnetism The palaeomagnetism in the basaltic rocks of an oceanic ridge, e.g. the North Atlantic Ridge, shows a pattern of stripes parallel to the median rift, alternate stripes having a reversed magnetism corresponding to the periodic reversal of the Earth's magnetic poles. It is found that matching patterns of stripes have the same sequence in opposite directions away from the median rift, and this was taken as independent evidence for ocean floor spreading. Plate Tectonics The idea was advanced that the outer shell of the Earth, the lithosphere, could be considered as a mosaic of twelve or more large rigid plates. These could move in three ways: (i) by one plate sliding past another along its margin; (ii) by two plates moving away from one another; (iii) by two plates moving together and one sliding underneath the edge of the other. Plate Tectonics