10.2 Earthquake measurement and location

Seismographs are crucial tools for measuring earthquakes. They detect ground motion, record seismic waves, and help scientists understand the Earth's inner workings. From mechanical to electronic types, these devices capture vital data about tremors and their impacts.

Earthquake intensity scales like the Richter and moment magnitude scales quantify quake strength. By analyzing seismograms and using techniques like triangulation, scientists can pinpoint epicenters and interpret seismic data, revealing valuable insights about our planet's seismic activity.

Seismographs and Earthquake Measurement

Functionality of seismographs

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• Seismograph components include seismometer detects ground motion and recording device preserves motion data
• Operating principle utilizes inertia of suspended mass creates relative motion between mass and ground
• Types of seismographs encompass mechanical seismographs use physical mechanisms and electronic seismographs employ digital sensors
• Recording process converts ground motion to electrical signals amplifies data then records digitally or analog
• Seismic wave types recorded include P-waves (primary) arrive first S-waves (secondary) follow and surface waves (Love and Rayleigh) travel along Earth's surface

Earthquake intensity scales

• Richter scale measures largest seismic wave amplitude uses logarithmic scale calculates local magnitude (ML) with formula $ML = \log A - \log A0$
• Moment magnitude scale assesses total energy released by earthquake calculates seismic moment (M0) with formula $M0 = μAD$ then determines moment magnitude (Mw) using $Mw = \frac{2}{3}\log M0 - 10.7$
• Comparison between scales shows Richter scale saturates around magnitude 6.5-7 while moment magnitude scale has no upper limit providing more accurate measurements for large earthquakes

Locating earthquake epicenters

• Principle of triangulation employs at least three seismic stations measures time differences between P-wave and S-wave arrivals
• Travel-time curves graphically represent wave arrival times vs distance help determine epicentral distance
• S-P interval method calculates epicentral distance using formula $Distance = (S-P interval) × (Velocity factor)$
• Circle method involves drawing circles around each station with radii equal to calculated distances locates epicenter at intersection of circles

Interpretation of seismograms

• Seismogram components include time axis amplitude axis P-wave arrival and S-wave arrival
• Distance determination measures S-P interval uses travel-time graphs or tables applies S-P interval method
• Direction determination analyzes first motion compares amplitudes between horizontal components
• Additional seismogram features show surface wave arrivals coda waves and background noise provide further insights into earthquake characteristics