1. Seismic Intensity: a measure of violence of ground shaking (based on damage done to human-made structures, surface changes, and felt reports). Intensity varies with distance from the hypocenter and ground conditions. Isoseismals-lines of equal seismic intensity. Modified Mercalli Intensity Scale: I-XII (no units) _________________________________ Seismic Magnitude - a unique measure of the energy released or size (based on logarithm of maximum body waves or surface wave amplitude on seismographs). M L Richter Magnitude S-waves (no units) m b Body wave magnitude P-waves “ M S Surface wave magnitude Rayleigh waves “ M o Seismic moment (units of Newton-meters) = (shear modulus * area * slip) M W Moment Magnitude (no units)

2. Modified Mercalli Intensity Scale (1902) [MMI-Unitless] I. People generally do not feel any shaking. II. A few sensitive people might feel shaking. III. Many people feel shaking; hanging objects sway. IV. Most people indoors feel shaking; hanging objects swing; dishes rattle. V. Almost everyone feels shaking; doors swing; dishes break; pictures move; no structural damage. VI. Everyone feels shaking; objects fall from shelves; pictures fall off walls; furniture moves. Plaster in walls might crack. VII. People have difficulty standing. Drivers feel their cars shaking. Some furniture breaks; bricks fall from buildings; buildings damaged. VIII. Houses not bolted down may shift on their foundations; towers and chimneys twist and fall; buildings damaged. IX. Well-built buildings suffer considerable damage; pipes break. X. Most buildings & foundations destroyed; bridges destroyed; dams damaged; large landslides. XI. Most buildings collapse; bridges destroyed; large cracks in ground; pipelines destroyed; railroad tracks bent. XII. Almost everything totally destroyed; objects thrown into air; ground moves in waves or ripples. MMIpeak velocity acceleration (cm/sec ) near epicenter ( fraction of g) I-IV. 1-20.015-0.02g V. 2-5 0.03-0.05g VI. 5-80.06-0.09g VII. 8-120.1-0.19g VIII. 20-300.2-0.3g IX. 500.3-0.5g X. 60-800.6-0.9g XI.-XII. >100>1g

3. Richter Magnitude Nomogram

4. 1994 Northridge CA Earthquake

5. VII VI

6. 13Aug1886: Charleston, SC M w =7.5

7. Do sleeping pets sense earthquakes? It depends on their size…

8. Similar Magnitude Eqs but Totally different Isoseismals Due to differences in lithosphere structure & rigidity New York City Earthquake of August 10, 1884

10. Earthquake m b M S FSArea offset M o M w (km) (m) (N-m) Loma Prieta 1989 6.2 7.1 40x15 1.7 3.0e19 6.9 San Francisco 1906 -- 7.8 450x10 4 5.4e20 7.8 Alaska 1964 6.2 8.4 500x300 7 5.2e22 9.1 Chile 1960 -- 8.3 800x200 21 2.4e23 9.5 Moment Max MM# EQEQ Name & Effects Magnitude Intensityper year 1-1.9I ~3,000,000 Tiny- recorded if instrument is close 2-2.9II~350,000Very Minor- Generally not felt indoors, but recorded. 3-3.9III~50,000Minor- Generally not felt, but recorded. 4-4.9 IV-V ~6,000 Light- Often felt, but rarely causes damage. 5-5.9VI-VII~800Moderate- Slight to major damage to buildings. 6-6.9VII-VIII~300Strong- Can be destructive within ~80 km. 7-7.9IX-X~20Major- Can cause serious damage. >8 XI-XII~1Great- Can cause very serious damage. The Moment Magnitude scale is not a simple logarithmic scale (factor of ten) with respect to energy- M W 4---------5--------6--------7--------8 Energy Ratio 48 43 39 35 M w 6 EQ = the energy of ~2050 * M w 4 EQ