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Magnitude: measuring the amplitude of seismic waves Measured by seismograph Scaled on the Richter scale – Logarithmic scale: for each increase of 1 point, the earthquake is 10 times stronger A 5.0 earthquake is 10x stronger than a 4.0 A 8.0 earthquake is 100x stronger than a 6.0 Seismograph: Records the motion of the earth, and thus the seismic waves Seismograph Reading P-waves arrive first, then S waves, the Surface waves (love and rayleigh) Seismograph recording stations will record the time between the arrival of P waves and S waves to determine how far away the epicenter is – Longer time between the waves means the earthquake is further away 3 seismograph readings are used to find the epicenter Each site determines its distance from the EQ and maps it as a radius around the site The place where all circles intersect is the epicenter Distance is different at each of these sites, but magnitude reading is the same. Intensity: Measure of damage or shaking an earthquake causes Scaled on the Mercalli Scale Given based on observation of damage, so values are different in different locations – Closer to the epicenter = higher intensity rating Mercalli Scale rates EQs 1-12 Northridge Earthquake Intensity Haiti Earthquake Intensity Volcanoes Hills or mountains that erupt lava Formed at divergent and convergent plate boundaries Divided into two categories: – Steep slope – Gentle Slope Steep Slope Volcanoes Composite volcanoes are also known as stratovolcanoes Steep Slope Volcanoes Viscous (thick) lava – Does not flow easily (think of syrup or tar), so builds up on the sides of volcanoes. This is what creates the steep slope – What happens when you blow bubbles in syrup? Gas gets trapped in the viscous lava – Causes VIOLENT eruptions! Steep Slope Volcanoes Form at convergent boundaries – Pressure built up under subduction zones causes violent eruptions Ring of Fire: active volcanoes surrounding the convergent boundaries that border the Pacific Ocean Gently-sloped Volcanoes Gently-Sloped Volcano Lava is not viscous (Not thick; runny) – Flows easily down the volcano, so gentleslope is formed – Gas not trapped in lava (think of blowing bubbles in water) Eruptions are calm (no pressure built up from gas) Lots of Lava when it erupts! Gently-sloped Volcanoes: Form at divergent boundaries or Hot Spots (This is what formed Hawaii!) Hot Spots: Very hot regions in earth’s interior •Hot spots stay in the same place, but plates move over them •This forms volcanic island chains, such as Hawaii