Geohazards Flashcards
geohazard
a geological condition that is dangerous to the environment and the people who live in it
elastic rebound theory
Rocks bend until strength of rock is exceeded. Rupture occurs + rocks quickly rebound to an undeformed shape. Energy released in waves that radiate outwards. How rocks behave depends on force applied, their competency + depth.
What are the effects of earthquakes on the built environment? x4
bricks+ stonework separate along mortar= wall collapse
floors separate from supporting walls, pancaking on top of each other
sectional bridges separate from supports
utility pipes separate + leak
attenuation
loss of energy experienced by a wave shown as a reduction in amplitude as it propagates through a material
why do incompetent rocks have more attenuation and in competent rocks its negligible?
incompetent- absorb more energy
competent- allow waves to pass through with almost no loss of energy
liquefaction
saturated unconsolidated material losing strength and rigidity in response to an applied stress e.g. earthquake
How can buildings be designed to counteract the effect of vertical and horizontal stresses? x4
Choose height of building so natural and local frequency of seismic waves don’t match
Symmetrical buildings distribute stresses equally
Avoid ornamentation which can be dislodged
Buildings should dissipate some energy by undergoing plastic flow e.g. pre formed beams or wooden structures
what is the aim of ground or base isolators?
separate vibrating ground from building
How can a building be built to resist shear forces? x4
framework strengthened with diagonal cables or rigid girders
large open spaces avoided
floors fixed to walls to prevent pancaking
shear walls with no openings extended to full height or building
How are buildings designed to absorb sway? x5
flexible supports and materials hydraulic systems flexible connection active movement damping controlled rocking frame
active movement damping
Heavy mounted mass on top of building and connected to dampers. When building begins to oscillate, mass moves in opposite direction, reducing amplitude of mechanical vibrations
controlled rocking frame
Steel frame, cables and shock diffusers. During earthquake, frames rock up and down directing energy down to diffusers. Steel teeth in diffusers grind together. Shaking stops- cables pull building upright.
seismic risk
the possibility of death, injury or damage that may occur with a certain period of time
how can seismic risk be reduced?
enforcing up to date building code
improving emergency response and basic infrastructure
preparing for emergencies which will arise after earthquake
How is a seismic risk assessment carried out? x7
hazard maps given to e.g.engineering + logistics experts
public education programmes communicate plans
immediate risk passed to public by emergency services
info from historical records added to hazard map
1 degree of intensity added to scale to give a safety margin
other maps show geological features
areas previously effected compared to similar areas
