Are Creeping Faults at Risk of Rupturing?

A new Cal Tech study using earthquake simulations has provided very strong evidence for a form of earth movement that may have been involved in the Japan 2011 Quake and Tsunami. This quake was a 9.0 magnitude quake. The study involves a little known type of gravel known as rock gouge which is sized in the micrometer range.

The Japan 2011 quake is one of the most destructive earthquakes to have hit modern society. The quake triggered an ensuing Tsunami and a significant nuclear accident. Learning more about the cause of this great quake could signficantly help earthquake insurers, people, and governments around the world.

It All Starts with the Gravel:

It has been speculated that a type of gravel has a specific influence on earthquakes. This gravel is exceptionally small. This gravel is known as rock gouge. It has both the ability to halt earthquakes and yet “triggers the rebirth of earthquakes” in an explosive way. Rock gouge is a very small material but can play a large role in earth movement. Apparently though it can have a large effect on earth movement.

It seems that Rock Gouge is a type or kind of Fault Gouge. Fault gouge is explained by wikipedia as “a tectonite with a very small grain size.” It also states that it “has no cohesion and it is normally an unconsolidated rock type, unless cementation took place at a later stage.”

How Rock Gouge Interacts with Earth Movement:

Rock Gouge is pretty complicated in terms of how it interacts with earthquakes and land movement. In the beginging the unusual gravel works to stop quakes by acting as a “barrier to the rupture” and by “absorbing energy” and stopping movement. Later when the plates begin to move past one another the gravel interface weakens and “dramatically reduces friction between the two plates, causing the re-emergence of the quake. This process is known as “renucleation.”

Therefore the most important thing to understand here may be that the “renucleation” “dramatically reduces friction between the two plates” and may cause a new second “quake.” Therefore initially rock gouge may stop quakes, but later on may end up causing new earth movements.

The Tools of the Experiment

To conduct this experiment the team used “Caltech’s so-called seismological wind tunnel. [Its not really a wind tunnel.]” The earthquake researchers also used homalite and a “fine-grained quartz powder” to conduct their highly specialized and imaged seismic test. This test was completed inside a labratory with numerous measurement tools. Tests of this type are sometimes referred to as “Lab Earthquake” tests. Lab earthquake tests allow for experiments to be explored that were not previously possible.

The name of the paper in Nature Magazine is: Intermittent lab earthquakes in dynamically weakening fault gouge. Nature is a British scientific publication that has roots going back to the 1860s.

The Rock Gouge Earthquake Conclusion:

Rock Gouge is a “a micrometer-sized granular material.” This gravel has been the source of speculation for years in terms of how it is involved with land movement and earthquakes. The conclusions for this study are important for all things earthquake related. “Based on the previous rich body of rock-friction experiments, we know that rock gouge can either strengthen with fault slip and act as a barrier, or weaken and promote earthquake rupture,” Lapusta says. “

What Does this Report and Rock Gouge Say about the Earthquake Insurance Marketplace:

At the current time, the report Earthquakes Show How Grains at Fault Boundaries Lead to Major Quakes has not changed earthquake insurance issuance. However it is expected that the relevant information concerning rock gouge and its properties will be incorporated into insurer’s risk modelling. Likely at some future time. It is possible that some insurers may use the new found data, while others may not. Soil composition type is a characteristic with at least one major earthquake vendor currently. Our estimate is that more property insurers will be considering soil in their underwriting decisions. After reading this report – why wouldn’t you?

Source of Information on reeping Faults at Risk of Rupturing?

Science Daily: Lab earthquakes show how grains at fault boundaries lead to major quakes

Nature Magazine: Intermittent lab earthquakes in dynamically weakening fault gouge