Reason Magazine 2014 Quartal 2 Seite 32

Hinweis: Dies ist eine maschinenlesbare No-Flash Ansicht.
Klicken Sie hier um zur Online-Version zu gelangen.

Inhalt

A FEW GREAT SHAKES Lessons learned following the magnitude 5 8 Virginia USA earthquake and the ground motion amplification caused by soft soil This summer marks the three year anni versary of the August 2011 magnitude 5 8 Virginia earthquake The U S Geological Survey USGS located the event in Louisa County 37 miles 60 kilometers northwest of Richmond Virginia and 84 miles 135 kilometers southwest of Washington D C at a depth of 3 7 miles 6 kilometers This particular earthquake occurred in the Cen tral Virginia Seismic Zone an area known to produce small earthquakes every few years Prior to the 2011 earthquake the largest earthquake on record in the Central Virginia Seismic Zone occurred in 1875 clocking in at 4 8 magnitude The damage resulting from the earthquake included bricks falling from chimneys broken plaster destroyed windows and overturned furniture in some homes The 2011 Virginia earthquake is the largest event in the central and eastern U S since the 1897 magnitude 5 9 Giles County Virginia earthquake see Figure 1 The regional geologic structure and faults run southwest northeast parallel to the Appalachian Mountains The faults are ancient and most are considered inactive Since no surface rupture from the 2011 Vir ginia earthquake has been discovered and the area is not covered by detailed geologi cal maps it is difficult to designate a specific causative fault for the earthquake Ground Shaking The Did You Feel It DYFI program developed by the USGS in the late 1990s allows people to record their earthquake experiences online The program uses the Modified Mercalli Intensity MMI scale see Figure 3 Using the MMI the intensity or the effect of an earthquake on the earth s surface is measured in 12 increasing levels of intensity able to be observed by people without special instruments or training The levels of intensity range from minimal shak ing to total damage The MMI at each location is determined from people s responses After the 2011 Vir ginia earthquake over 148 000 people in the eastern United States and Canada rushed AP Photo J Scott Applewhite File theSCIENCE 32 Reason ISSUE 2 2014