Earthquake Directivity Effects

Understanding Earthquake Directivity

Directivity is a fundamental effect where the direction of fault rupture strongly influences the intensity and duration of seismic shaking at different locations.

Key Physical Mechanisms:

• Forward Directivity: Stations in the direction of rupture propagation experience amplified, shorter-duration shaking
• Backward Directivity: Stations opposite to rupture direction see longer-duration, lower-amplitude waves
• Doppler Effect: Rupture velocity approaching the speed of seismic waves creates frequency shifts
• Constructive Interference: Waves from different parts of the fault arrive nearly simultaneously in forward direction

Practical Importance:

• Earthquake Engineering: Buildings in forward directivity zones experience much stronger shaking
• Seismic Hazard: Directivity can amplify ground motion by factors of 2-4 or more
• Rupture Imaging: Directivity patterns help determine fault orientation and rupture direction
• Real-time Seismology: Understanding directivity improves earthquake early warning systems

Interactive Features: Click on stations to see their seismograms. Adjust rupture parameters to explore how fault geometry and rupture velocity affect directivity patterns. Notice how forward directivity creates sharp, high-amplitude pulses while backward directivity produces extended, lower-amplitude signals.