Lab 16: Earthquake Hazards and Human Risks

 

Objectives:

-          Review types of faults and plate boundaries

-          Discuss earthquake terminology

-          Differentiate between different body waves

-          Discuss reading a seismogram

 

Introduction:

            Earthquakes: shaking and vibrations of the Earth, caused by large releases of energy

                        - accompany volcanic eruptions, explosions, and movement along faults

            Richter scale: logarithmic scale for measuring the strength of earthquakes

            Focus (foci): point of origin for an earthquake

                        - radial expansion from focus

                        - Mexico City, 9500 deaths in 400 km radius, could not feel in PA 3200 km away

            Hazards: destruction of buildings, breakage of pipes, electrical lines, development of

fissures, change in the course of streams, generation of tsunamis

            Strength of wave dependent on material it is passing through

                        - loose unpacked sediments will shake more, cemented sediments will not

                        - control high or low damage from the same strength earthquake

 

Graphing seismic data and locating epicenters:

            Epicenter: the point on the Earth’s surface at or above the earthquake’s focus

            Seismogram: a record of seismic wave motions obtained at a specific recording station

            Body waves: seismic waves that travel through the Earth’s interior

                        P-wave: primary, travel fastest, arrive first (compressional, push-pull waves)

                        S-wave: secondary, travel slower, arrive after P waves (shear, side to side waves)

                        L-wave: love waves, travel slowest, arrive after S waves, travel along the surface

            Arrival time: time when each wave reaches a seismic station

            Travel time: time from start of wave to measuring destination

            Distance from epicenter: distance from seismic station to epicenter

            Can calculate rate of travel (rate = distance/time)

 

Other analyses:

            Active faults: faults that can move and generate earthquakes at the present time

            First motion: can be identified as compressional or dilational based on P wave

                        - P-wave up, compression

                        - P-wave down, dilational

            Blind faults: faults that do not emerge at the Earth’s surface