UNIVERSITY OF SOUTH ALABAMA GY 111 Physical Geology Last time Faults Brittle Deformation A Types of Brittle Deformation B Types of faults terminology C Faults on maps Lecture 24 Earthquakes Brittle Deformation When rocks break one of 3 things can occur 1 cracking fracturing 2 jointing 3 faulting Brittle Deformation Faults come in two main flavors Dip Slip movement is in the direction of the dip of the fault plane Strike Slip movement is in the direction of the dip of the fault plane Fault Terminology All faults share some features Faults on Maps There is a special class of reverse fault that is common in mountain belts Thrust Faults All active faults are subject to earthquakes 1 Today s Agenda Earthquakes A Seismic waves and the Earth s interior B Earthquake intensity and magnitude C Seismographs and locating earthquake epicenters on maps D Case Studies Internal guts of the Earth The 4 layers of the Earth are distinguished on the basis of geophysics specifically the way that seismic waves travel through the Earth Web notes 24 GY 111 Lab Manual Chapter 7 Seismic Waves Three major types of seismic waves are distinguished Seismic Waves P and S waves are called body waves because they travel through the Earth 1 P waves Primary travel by compression 2 S waves Secondary travel by shear 3 Surface waves Long waves travel along the surface P waves travel through all media and are the fastest 4 km s S waves cannot pass through liquids and are slower 3 km s Seismic Waves Seismic Waves As P and S waves travel through the Earth they speed up and slow down according to the density of the materials they pass through This results in wave refraction Surface Long waves are also divisible into 2 types according to vibration direction don t worry about this for any tests If an earthquake is powerful enough seismic waves can make it around the world Propagation of P waves 2 Seismic Waves But wave refraction results in the formation of shadow zones where P or S waves do not occur Seismic Waves But wave refraction results in the formation of shadow zones where P or S waves do not occur The S wave shadow zone is wider than the P wave shadow zone P wave shadow zones Seismographs Seismic waves are recorded using seismographs P wave shadow zones Seismographs Seismic waves are recorded using seismographs The traces are called seismograms More about seismograms shortly but first Earthquake magnitude Earthquake Magnitude Earthquake Magnitude The intensity of an earthquake can be measure through one of two ways 1 A people method Modified Mercalli Intensity Scale I to XII 2 A geophysical method Modified Richter Scale 1 to 10 3 Earthquake Magnitude The Modified Mercalli Intensity Scale is most useful for historical earthquakes but is subject to perception errors Earthquake Magnitude The Modified Richter Scale uses geophysical information recorded from seismographs You need to measure the amplitude but also take into account the distance from the earthquake epicenter Earthquake Magnitude Earthquake Magnitude You need to measure the amplitude but also take into account the distance from the earthquake epicenter Earthquake Magnitude Magnitude 1 Effects source http earthquakescanada nrcan gc ca Not perceptible to people 2 3 Often felt but rarely cause damage 4 Earthquakes per year worldwide Source USGS Strength compared to a Magnitude 3 quake 100 1 300 000 10 130 000 13 000 10 5 At most slight damage to well designed buildings Can cause major damage to poorly constructed buildings over small regions 1300 100 6 Can cause damage to poorly constructed buildings and other structures in areas up to about 100 kilometers across where people live Substantial deaths especially if epicenter is in a major city 150 1000 7 Major earthquake Can cause serious damage over larger areas 20 10 000 8 Great earthquake Can cause serious damage and loss of life in areas several hundred kilometers across 1 100 000 9 Rare great earthquake Can cause major damage over a large region over 1000 km across 1 1 000 000 10 Impossible unless you make bad movies 10 000 000 4 Earthquakes In the USA 1973 2002 Earthquakes In the USA Earthquakes In the USA Death 101 The Earthquake Edition Woodcut New Madrid 1812 Three earthquakes all above 9 hit the New Madrid area from 18121813 Their cause is still debated Source http quake wr usgs gov prepare factsheets NewMadrid Woodcut gif Death 101 The Earthquake Edition Death 101 The Earthquake Edition Magnitude vs Ground Motion and Energy Magnitude San Francisco 1906 Average Annually 8 10 1 7 7 9 17 6 6 9 134 5 5 9 1319 4 4 9 13 000 estimated 3 3 9 130 000 estimated 2 2 9 1 300 000 estimated Based on observations since 1900 Based on observations since 1990 Source http neic usgs gov neis eqlists 5 Death 101 The worst earthquakes as far as death is concerned Date Location Deaths Jan 23 1556 Shansi China 830 000 8 July 27 1976 Tangshan China 255 0001 7 5 Date Location Deaths Jan 23 1556 Shansi China 830 000 July 27 1976 Tangshan China 255 0001 Aug 9 1138 Aleppo Syria 230 000 n a 7 5 Aug 9 1138 Aleppo Syria 230 000 n a Dec 26 2004 off west coast of northern Sumatra 225 000 9 0 Dec 22 8562 Damghan Iran 200 000 n a May 22 1927 near Xining Tsinghai China 200 000 7 9 Dec 26 2004 off west coast of northern Sumatra 225 000 9 0 Dec 22 8562 Damghan Iran 200 000 n a May 22 1927 near Xining Tsinghai China 200 000 Dec 16 1920 Gansu China 200 000 March 23 8932 Ardabil Iran 150 000 7 8 Dec 16 1920 Gansu China 200 000 7 8 n a March 23 8932 Ardabil Iran 150 000 n a Sept 1 1923 Kwanto Japan 143 000 7 9 Sept 1 1923 Kwanto Japan 143 000 Oct 5 1948 Ashgabat Turkmenistan USSR 110 000 Dec 28 1908 Messina Italy 70 000 100 0003 7 9 7 3 Oct 5 1948 Ashgabat Turkmenistan USSR 110 000 7 3 7 2 Dec 28 1908 Messina Italy 70 000 100 0003 Sept 1290 Chihli China 100 000 7 2 n a Sept 1290 Chihli China 100 000 n a Oct 8 2005 Pakistan Nov 1667 Shemakha Caucasia Nov 18 1727 Tabriz Iran 80 361 7 6 Oct 8 2005 Pakistan 80 361 7 6 80 000 n a Nov 1667 Shemakha Caucasia 80 000 n a 77 000 n a Nov 18 1727 Tabriz Iran 77 000 n a Dec 25 1932 Nov 1 1755 May 31 1970 Gansu China 70 000 7 6 Dec 25 1932 Gansu China 70 000 7 6 Lisbon Portugal 70 000 8 7 Nov 1 1755 Lisbon Portugal 70 000 8 7 Peru 66 000 7 9 May 31 1970 Peru 66 000 May 30 1935 7 9 Quetta Pakistan 30 000 60 000 7 5 May 30 1935 Quetta Pakistan 30 000 60 000 7 5 Locating Epicenters on maps Magnitude Death 101 The worst earthquakes as far as …