Using centroid time-delays to characterize source durations and identify earthquakes with unique characteristics

- We use centroid time-delay measurements to study temporal source characteristics of earthquakes.
- Time-delays are measured for all Mw≥6.5 earthquakes between 1990 and 2012 at a global scale.
- We present a simple scaling relationship between the scalar seismic moment and the time-delay.
- Using this standard relationship, we can investigate variations in the stress parameter ∆σ.
- We can also identify unusual events with atypical rupture velocity, stress drop or aspect ratio.

The relationship between M0 and the rupture duration is often difficult to establish. This is particularly true for large earthquakes for which the moment rate functions (MRF) generally have complicated shapes, and the estimated durations can vary considerably depending on the methodology used to evaluate the MRF. In this work, we show that the centroid time-delay (τc) provides an alternative estimate of the source duration. Inverted MRFs often end gradually, making the end of coseismic rupture difficult to detect. In such cases, when the rupture duration is not well defined, the time-delay τc is a useful quantity to represent the first-order temporal characteristics of the rupture process. Variations in stress parameter Δσ can be investigated by assuming a standard scaling relationship between the seismic moment M0 and τc. This simple scaling relationship can also be used to identify unusual earthquakes, with unique source properties, such as events involving complicated rupture processes or earthquakes characterized by unusual rupture velocities, stress drops or aspect ratios.