ANNOUNCEMENTS Generally speaking, you have to give it a week to get your exams back… If you are wildly curious, me any time after the weekend and hopefully I’ll have yours graded! Between one thing and another I have nearly everyone’s PIN now, but if you haven’t sent it yet, you can’t take the next exam (whenever that is…)

TODAY The earthquake “cycle” (elastic rebound) Kinds of earthquake waves The relation between depth and intensity

Clickers please…

Overall, how was the exam? 1.Too easy 2.Easy enough 3.Hard, but challenging, so okay 4.Too hard

Please click whichever is correct for you 1.True -- I got the 2 points of extra credit for reading the directions and putting in my initials in the space 2.False -- what 2 points? 3.False -- I’m moderately bad about reading directions…

The “earthquake cycle”, usually called “elastic rebound” -- how stress is applied to rocks until they break

What happens when rocks break? remember the little radio tower with the waves coming out in all directions

I. waves INSIDE the earth

I. waves ON the SURFACE of the earth (put these two motions together…)

Clickers…

Seismologists tell us the outer core is molten. What aspect of earthquake waves supports this hypothesis? 1.P waves going through the center of the earth arrive faster on the exact opposite side 2.P waves vanish when going through the center of the earth 3.S waves going through the center of the earth arrive faster on the exact opposite side 4.S waves vanish when going through the center of the earth

What probably happens to wave speed in the asthenosphere? 1.They all slow down 2.They all speed up 3.Only P waves slow down 4.Only P waves speed up 5.Only S waves are affected

Creep

Clickers…

What kind of fault is creeping in this picture? A.A normal fault B.A reverse fault C.A left-lateral strike-slip fault D.A right-lateral strike-slip fault

(how to try to predict an earthquake) How to predict an earthquake

Ground deformation: the Palmdale Bulge Located some 35 miles north of downtown Los Angeles at the edge of the Mojave Desert, Palmdale (pop. 13,500), Calif., is a sleepy town where the loudest sounds are usually the whistling of desert winds and the popping noise of exhausts as teen-age dragsters race their cars. But Palmdale has been lifted, quite literally, out of obscurity. Scientists have recently discovered that it is in the center of a 120-mile-long, kidney-shaped area of land that rose as much as ten inches in the early 1960s. The phenomenon has earned the desert town a dubious notoriety. The Palmdale bulge, as the uplift is called, could be an early warning signal of a major — and potentially disastrous — earthquake. Recent studies have shown that the ground rose noticeably before the 1971 San Fernando quake that killed 58 people in California's last major trembler. Before a 1964 quake that destroyed much of Niigata, Japan, the ground lifted two inches, and the Chinese discovered an elevation of the land in Liaoning province before the Manchurian earthquake of February TIME magazine, April, 1976

SAN ANDREAS FAULT

Ground deformation: the Palmdale Bulge

The results: land to the NE of the fault subsides, but nothing necessarily associated with the earthquake

Foreshocks (or the earthquake itself?) Water wells Animals