🌍 Earthquake Relative Relocation: HypoDD Method

Harvard EPS55

Understanding Double-Difference Relocation

The HypoDD method improves earthquake location accuracy by using relative positioning instead of absolute positioning. It minimizes location errors by analyzing the differences in travel times between nearby earthquake pairs at common stations.

Original Locations (Absolute)

Relocated (HypoDD)

Seismic Stations

True Locations

Animation Speed: 800 ms

Location Error (km): 2 km

Number of Earthquakes: 25

Before Relocation (Absolute Positioning)

After HypoDD Relocation (Relative Positioning)

📊 Relocation Statistics

Mean Location Error

RMS Improvement

Relocated Events

Current Iteration

Total Iterations

RMS Residual

🔬 How HypoDD Works

Double-Difference Principle: Instead of computing absolute travel times from earthquakes to stations, HypoDD uses the difference between travel time differences. For earthquakes i and j recorded at stations k and l:

dr = (t_ik - t_jk) - (t_il - t_jl)

Key Advantages:

🎯 Cancels systematic errors: Velocity model uncertainties and station timing errors are minimized
🔗 Relative constraints: Uses spatial relationships between nearby events
📈 Improved precision: Typically achieves sub-kilometer accuracy for clustered events
⚡ Iterative refinement: Progressively improves locations through multiple iterations