Geology and Earth Structure

A major earthquake did strike Qinghai province in China in 2010, registering 6.9-7.1 magnitude and causing significant damage and casualties. However, it occurred on April 14, not April 13. The one-day difference makes the statement false.

The massive 8.8-magnitude earthquake occurred in Chile on February 27, 2010, not February 18. This was one of the most powerful earthquakes ever recorded and triggered tsunami warnings across the Pacific Ocean. Over 500 people were killed, and the earthquake caused widespread destruction in central Chile, particularly affecting the cities of Concepción, Talcahuano, and Santiago.

P-waves (primary waves) are the first seismic waves recorded during an earthquake because they are compressional waves that travel fastest through Earth's materials. S-waves (shear waves) arrive later, followed by surface waves (L-waves) which cause the most damage.

The Mercalli scale measures earthquake intensity based on observed effects and damage at specific locations. The Richter scale measures magnitude (energy released), while a seismograph is an instrument that detects and records seismic waves, not a measurement scale.

A fathometer is an echo sounder used to measure water depth in oceans and lakes. It works by sending sound waves to the ocean bottom and measuring the time for the echo to return - this is called sonar (Sound Navigation and Ranging).

A seismograph is an instrument that detects and records ground motion caused by seismic waves from earthquakes or explosions. It typically consists of a frame attached to the ground and a suspended mass that remains stationary during ground movement, creating a relative motion that is recorded as a seismogram, allowing scientists to measure earthquake magnitude and analyze wave characteristics.

The Richter scale is a logarithmic scale ranging from 0 to 10 that measures the magnitude of earthquakes based on the amplitude of seismic waves recorded by seismographs. Each whole number increase represents a tenfold increase in measured amplitude and approximately 31.6 times more energy release. Earthquakes below 2.0 are rarely felt, while those above 7.0 cause major damage.

Earthquakes primarily occur at tectonic plate boundaries where plates interact, collide, or slide past each other. The immense stress buildup and release along these boundaries causes the majority of seismic activity. Plate interiors have fewer earthquakes because they are more stable and under less tectonic stress.

P-waves (primary waves) are the fastest seismic waves and therefore reach seismographs first after an earthquake occurs. They travel through both solid and liquid materials and move in a compressional motion. The time delay between P-waves and slower S-waves helps scientists determine earthquake distance.

S-waves (shear waves) cannot propagate through fluids because fluids cannot sustain the shearing motion that S-waves require - they have no shear strength. P-waves can travel through all materials, including fluids. This property of S-waves helped scientists discover that Earth's outer core is liquid.

Three seismograph stations are needed to locate an earthquake's epicenter through triangulation. Each station provides a distance circle, and where all three circles intersect is the epicenter location. Two stations give two possible intersection points, while one station cannot determine location at all.

A majority of earthquakes (over 80%) do occur in the sea along oceanic plate boundaries. Earthquake waves don't always make audible noise, not all quakes kill people, and scientists do understand what causes earthquakes (plate tectonics). The oceanic statistic is the only accurate statement among the options.

The San Andreas Fault is a major transform fault boundary running through California that is responsible for many earthquakes in the region. The Alpine fault is in New Zealand, Great Glen fault is in Scotland, and Hope fault is also in New Zealand. California's seismic activity is dominated by the San Andreas system.

The Richter scale is logarithmic, meaning each whole number increase represents 10 times greater ground motion. Going from magnitude 6 to magnitude 8 is a 2-unit increase, so the motion is 10 x 10 = 100 times greater. This is a key property of logarithmic scales that students must understand.