Introduction to Earthquake Engineering

Introduction to EARTHQUAKE ENGINEERING  LEARNING OBJECTIVES: At the end of the lesson, you should be able to: 1. Develop a meaningful understanding of AGENDA 2. earthquake and earthquake engineering Discuss the different terminologies in...

Introduction to EARTHQUAKE ENGINEERING  LEARNING OBJECTIVES: At the end of the lesson, you should be able to: 1. Develop a meaningful understanding of AGENDA 2. earthquake and earthquake engineering Discuss the different terminologies in earthquake engineering 3. Explain the causes of Earthquakes and Faulting EARTHQUAKE -are broad-banded vibratory ground motions, resulting from a number of causes including tectonic ground motions, volcanism, landslides, rock bursts, and man-made explosions EARTHQUAKE TERMINOLOGIES EPICENTER – the geographical point on the ground surface where an earthquake is estimated to be centered FOCAL DEPTH – used to classify earthquakes as: shallow for focal depths less than 70 km (43 miles), intermediate for focal depths between 70 km (43 miles) and 300 km (186 miles), and deep for focal depths greater than 300 km (186 miles)  EARTHQUAKE DIP ANGLE – an angle with respect to the ground surface from which the plane slips or ruptures TERMINOLOGIES STRIKE ANGLE – The angle the fault plane makes with respect to the north direction along the surface  FAULT LINE – A long crack in the surface of the EARTHQUAKE earth. TERMINOLOGIES FAULT PLANE – The plane along which the rock ruptures and slips  EARTHQUAKE EPICENTER DISTANCE – the ground TERMINOLOGIES distance from the epicenter to a specified point. Causes of Earthquakes and Faulting In a global sense, tectonic earthquakes CAUSES OF result from motion between a number of large plates comprising the earth’s crust or EARTHQUAKES lithosphere (about 15 large plates, in total) AND FAULTING  CAUSES OF Tectonic plates move due to convective EARTHQUAKES motions in the Earth’s mantle, driven by AND FAULTING heat from the core. Friction and asperities at fault interfaces constrain this motion, but strain energy builds up until it overcomes resistance, causing a sudden slip known as elastic rebound, which releases energy as an earthquake. The initial rupture point is the hypocenter, and the CAUSES OF point directly above it on the surface is the epicenter. Energy is radiated over a broad EARTHQUAKES spectrum of frequencies through the earth, in body waves and surface waves (Bolt 1993). Body waves AND FAULTING are of two types: P waves (transmitting energy via push–pull motion) and slower S waves (transmitting energy via shear action at right angles to the direction of motion). Surface waves are also of two types: horizontally oscillating Love waves (analogous to S body waves) and vertically oscillating Rayleigh waves. Earthquakes occur most frequently at tectonic CAUSES OF plate boundaries, with the Pacific Plate’s boundary, known as the Ring of Fire, being EARTHQUAKES particularly active. This area includes Japan and the west coast of North America. While the AND FAULTING interiors of plates have low seismicity, they are not inactive. Tectonic plates move slowly and irregularly, causing frequent small and occasional large earthquakes. These movements can build up forces over time, leading to sudden, violent motions that produce shaking, causing damage to structures and triggering secondary hazards like landslides and tsunamis.  CAUSES OF Faults are typically classified according to EARTHQUAKES their sense of motion. Basic terms include transform or strike slip (relative fault motion AND FAULTING occurs in the horizontal plane, parallel to the strike of the fault), dip-slip (motion at right angles to the strike, up- or down-slip), normal (dip-slip motion, two sides in tension, move away from each other), reverse (dip-slip, two sides in compression, move toward each other), and thrust (low-angle reverse faulting).  CAUSES OF FOCAL MECHANISM EARTHQUAKES -refers to the direction of slip in an AND FAULTING earthquake and the orientation of the fault on which it occurs. Focal mechanisms are determined from seismograms and typically displayed on maps as a black and white ‘‘beach ball’’ symbol.  CAUSES OF EARTHQUAKES AND FAULTING  CAUSES OF SUBDUCTION EARTHQUAKES -refers to the plunging of one plate AND FAULTING (e.g., the Pacific) beneath another, into the mantle, due to convergent motion, as shown. Subduction zones are typically characterized by volcanism, as a portion of the plate (melting in the lower mantle) re-emerges as volcanic lava. Schematic diagram of subduction zone, typical of west coast of South America, Pacific Northwest of United States or Japan. ACTIVITY Draw a scene where an earthquake strikes in a normal fault, reversed fault, and slip- strike fault