Case studies of Earthquakes

           

1.  San Francisco Earthquake, April 18, 1906

            demonstrated connection between faults & eqs

            offset of earth surface  extending 400 km along trace of San Andreas Fault

            effect of ground shaking on unreinforced masonry

            Liquefaction: soils turn to 'quicksand', lose strength --> street collapse

            Fire:  major impact (secondary effect) <== severing of gas lines

                        unprotected wood frame buildings

                        rupture of water mains --> no water for fighting fires

            Disaster refugees:  thousands left homeless

 

2.  Anchorage, Alaska: March 27, 1964 (Good Friday EQ):

            Largest eq in history of U.S.  (Magnitude 9.1)

            Destroyed much of Anchorage (began modern eq hazard program)

                        rupture = 800 km long

                        uplift/subsidence affected 200,000 km2 

            Vertical displacements

                        uplifts to 6 m, disruption of shoreline

                        Subsidence --> flooding of coastal areas

            Building damage:  impact on modern city

            Landslide:  greatest impact, collapse of high bluffs above city

            Impacts on modern transportation system

            Tsunami:  EQ-triggered sea wave:  to 30 m high!

                        major impacts, ==> 120 deaths

                        impacts at large distances

           

3.  Mexico City:  Sept. 18, 1985  7:17 AM

            large eq (M7.8) at Pacific coast (near Acupulco)

                        --moderate damage at coast, severe damage at Mexico City

                        effects:  8000 dead, 30,000 injured, 50,000 homeless

            Collapse of mid-size buildings:  resonance!

            Vulnerable buildings:

                        higher skyscrapers, smaller buildings unaffected

                        10-14 story buildings resonate at 1-2 seconds = incoming wave period

            Mid-leval collapse:  <== pounding by neighboring buildings

            major damage at sites built on thick unconsolidated sediments

                        ==> importance of site amplification

                       

 

4.  Armenia 1988:  Dec. 7, 11:41 AM

            most severe event in USSR in 40 years

            enormous political/economic impact on USSR

            costs:  25,000 killed, 15,000 injured, 500,000 homeless, $14B damage

            Fault scarps:  intracontinental eq:  mostly vertical displacement

            modest size (~M7), but close to major cities

            Collapse of stone building:  traditional adobe/stone buildings, poorly

                                    reinforced --> total collapse

            effect of poor building practices

                        precast concrete slabs, held together by welds, rebar --> pancaking of floors

                        ==> poor design, shoddy workmanship, poor materials

           

           

5.  Loma Prieta:  October 17, 1989 (The World Series EQ!)

            M7.1 event near major US urban center

                        was this event predicted?

            effects:  $7 billion damage ($2.5billion in SF alone)

                        67 deaths, 500 homes, 100 buildings destroyed, 18,000/2,600 damaged

                        12,000 displaced

            Lessons:

                        Importance of EQ-resistant design

                        Importance of critical structures (41 deaths at Nimitz Freeway)

                              "           of emergency preparedness/education

                        Site amplification: major damage 80 km away from epicenter

                        Liquefaction effects