· Cause by movements of the tectonic plates around earth crusts
             · Most of them occur at boundaries of these plates. Ex. San Andres fault in California
             · 50% occur art sub duction zones concentrated along the ring of fire
             · In a volcano it could have more than a 100 earthquakes a day before an explosion
             · originate as magma work its way upward
             · pumping of waste fluid as it happened in Colorado
             Ø RICHTER SCALE ( American Francis Richter 1930,s)
             · It is a logarithmic scale runs from 1-9 measured 100km. from epicenter
             · A Magnt. 7 is 10 times more powerful than
             · a Magnt. 6, 100 times more powerful than a
             · a Magnt. 5, 1000 times more powerful than a
             · A magnitude 9.5 is now consider a practical limit
             It measures the intensity of shaking with roman numbers from I to XII
             · In 1975Chinese predict a 7.3 quake only two day after because of the chain of low- magnitude tremors called foreshokes
             · other way is analysing the bulging of the land surface and changes in earth magnetic fields
             · These shows there has been 4 magnitude 9.0 the las 40 years, meaning that there is one each decate around the world
             · Aprox. 100 quakes of magnitud 5-6 occur anually around the world
             · Aprox. 50 000 of magnitud 3-4
             ...