Beyond Fault Boundaries
Cascading Ruptures, in Japan and Venezuela
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Shortly after Venezuela’s earthquakes, we published a research note highlighting how ruptures may cascade through a connected fault system over a very short period of time, and we drew attention to the implications for the San Andreas fault system in California.
To recap:
- On June 24, Venezuela experienced a rare and destructive earthquake doublet
- A 7.2 foreshock was followed 39 seconds later by a 7.5 mainshock.
- Both earthquakes originated near the junction of the Boconó and San Sebastián faults
- Eastward propagation meant the seismic energy was directed towards Caracas.
- Stress-transfer models suggest the doublet has also increased stresses on unruptured segments of the San Sebastián fault beneath Caracas, creating the potential for future large earthquakes.
Kumamoto earthquakes in 2016 and 2026 provide additional data points to help understand how rupture and stress can move through a segmented fault network.
Kumamoto April 16, 2016: Fault-Junction Activation
A 6.2 foreshock on the northern Hinagu Fault was followed 28 hours later by a 7.0 mainshock near the fault junction and transferred onto the Futagawa Fault. Seismic and geodetic observations noted migrating seismicity, static stress changes and afterslip between the two events.
- Both events occurred within a segmented strike-slip fault system.
- The larger rupture moved through the Hinagu-Futagawa junction.
- The delay gave neighboring fault segments time to become more stressed before the mainshock
Kumamoto July 28, 2026: Adjacent-Segment Activity
A 6.8 mainshock was followed 41 minutes later by a 6.1 aftershock on another portion of the broader Hinagu fault system, southwest of the main 2016 activity. Although these events are best interpreted as a mainshock-aftershock sequence rather than a doublet, they do demonstrate continued activity within the same regional fault network, suggesting ongoing stress changes within the fault system.
What we learned
The three sequences are not identical, but collectively they show why the overall behavior of a connected fault system matters more than any one segment:
- Connected fault networks can transfer rupture or stress across the boundaries of mapped segments
- Progressive loading and transfer through a fault junction can occur (Kumamoto 2016)
- Adjacent parts of a fault network can remain active over longer timescales (Kumamoto 2026)
- A quick acting sequence makes dynamic triggering or a continuous cascading rupture more relevant than a slower afterslip-driven process. (Venezuela)
Please contact Haley Sisk, Research Analyst with any questions or comments on this topic.
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