Judith, I’ve kept this post open in Safari since you posted it so that I can refer to it when time allows. I contend that those of us “scientist-wanna-bes” wh find seismology compulsively engaging and wade through this particular material should be given an opportunity to be awarded a minor in geology just for “stick-to-itiveness” 😏. Thanks for this. Completely fascinating and informative. What a lab! What a lecture!
Anthroseismometers, huh? Thanks—that’s a great insight. I know the Japanese expression _ningen jishinkei_ (“human” + ”seismometer”) which without your anthroseismometer I probably would have rendered “walking seismometer”!
Details about the earthquakes are fascinating, as always!
This post has me thinking about what we really know about propagating fractures in earthquakes. Like what we saw in the video, the visible rupture is more often than not almost the last thing that happened. For example on a giant detachment fault such as the WHIPPLE MOUNTAINS in California, the last preserved actual fracture is razor sharp and it cuts through its own (microstructural) brecciation products. Same with pseudotachylites, the melt is forcefully injected along a fracture plane, and intrudes the adjacent country rock emanating from it. But given the speed of cooling, where was that melt created, and where is the evidence of the melting in the sidewalls to the razor sharp fractures from which it has injected into the sidewall?
Are there studies that unequivocally support the concept that a rupture propagates in the way as illustrated in the cartoon provided here? I am not sure. The problem comes down to the use of a principle loosely described as assuming a stochastic interdependence of space and time. Boiled down into a nutshell this principle asserts that the temporal evolution of a phenomenon (e.g. glacial valleys) can be worked out by observing the spatial variation of that same phenomenon, classifying the observed sequence in terms of rank order in terms of the stage of development, and then asserting that this same sequence is the temporal sequence by which this phenomenon progresses.
The method works to some degree, but in many aspects, it fails. The observed spatial variation is often the envelope of the paths taken through time, and it is often not true that the path taken through time must move along the envelope of the observed collection. In other words, as so often assumed in geology, time and space are not interchangeable, and this founding principle has been shown to fail on many an occasion. So is the case with trying to map the temporal evolution of a fault rupture by observing the envelope of fault products.
A rupture propagates quickly whereas it takes time for the movement to take place that generates the fault products. And many large faults have knife-sharp rupture planes when observed in outcrop, with clear evidence that the observed rupture cut through its own brecciation products?
So what are these observations telling us? That there are multiple brecciation episodes with late movement slicing on multiple ruptures. Certainly this is a model supported by the observations in doi:10.26443/seismica.v4i1.1691
A rupture propagates as long as it is driven, which in terms comes down to the lateral extent of the elastic energy stored in the rock mass prior to failure. I imagine that how the Earth works (and yes, I have been influenced by Per Bak) is to self-organise so that more and more energy is stored along a fault prior to its rupture, with an increasing lateral extent of the rock mass that is just below the critical yield stress that needs to be exceeded before catastrophic failure in its load bearing capacity is initiated. This buildup needs to happen over a long strike distance prior to onset of the earthquake.
Once catastrophic failure takes place locally, a triggering perturbation needs to propagate, if the rest of the strained rock mass is going to join the fray. This propagating perturbation could be the rupture front itself, as pointed out in the thought provoking article presented by Earthquake Insights.
But as suggested by doi:10.26443/seismica.v4i1.1691 super-shear ruptures also start in the far field, way ahead of the rupture front. So what is that about, if it is not caused by fast moving stress perturbations that locally trigger the onset of new ruptures in the far field, in the pre-stressed rock that sits waiting to fail. The thought provoking article presented by Earthquake Insights makes me wonder if the processes involved in creating this self-organised critical behaviour also include brecciation, and some prior movement on the structure that will eventually break.
To this intriguing debate please add doi:10.26443/seismica.v4i1.1691 with their abstract and summary as attached below. This adds yet another dimension to the debate, noting ruptures upon ruptures, and the comment that the total moment magnitude released may have been significantly under-estimated by conventional (point source) methodologies.
Abstract:
A large strike-slip earthquake occurred in central Myanmar on March 28, 2025. The aftershock distribution suggests that the rupture of the main shock propagated mainly to the south. However, a large amplitude phase lasting 20 s, followed by a short-period pulse-like phase, were observed at the stations on the north side of the source, while on the south side, multiple peaks without dominant phases continued for 90 s. Using the potency density tensor inversion method, we explain the ”unusual” waveform signature of the Myanmar earthquake by a multiple, asymmetric bilateral rupture, involving boomerang-like back-rupture propagation and supershear.
Non-technical summary:
On March 28, 2025, a large and devastating earthquake occurred in central Myanmar. We used globally observed seismic records to build the source process model of the large earthquake and reveal how the earthquake rupture evolved along the fault. We find that the earthquake ruptured a fault segment of 400 km length, in 80 s. Within the broad apparent southward fast rupture, the detailed rupture evolution was complex, being characterized by a series of discrete sub-events, involving bi-directional, southward and northward ruptures that migrated at fast speeds, partly faster than the seismic shear waves can travel. These findings are critical for our understanding of earthquake-rupture dynamics and assessing the associated earthquake hazard.
Judith, I’ve kept this post open in Safari since you posted it so that I can refer to it when time allows. I contend that those of us “scientist-wanna-bes” wh find seismology compulsively engaging and wade through this particular material should be given an opportunity to be awarded a minor in geology just for “stick-to-itiveness” 😏. Thanks for this. Completely fascinating and informative. What a lab! What a lecture!
This is an extraordinarily interesting post. Thank you so much for all the time and effort that went into it.
This is amazing levels of detective work!
Coolio
Anthroseismometers, huh? Thanks—that’s a great insight. I know the Japanese expression _ningen jishinkei_ (“human” + ”seismometer”) which without your anthroseismometer I probably would have rendered “walking seismometer”!
Details about the earthquakes are fascinating, as always!
This post has me thinking about what we really know about propagating fractures in earthquakes. Like what we saw in the video, the visible rupture is more often than not almost the last thing that happened. For example on a giant detachment fault such as the WHIPPLE MOUNTAINS in California, the last preserved actual fracture is razor sharp and it cuts through its own (microstructural) brecciation products. Same with pseudotachylites, the melt is forcefully injected along a fracture plane, and intrudes the adjacent country rock emanating from it. But given the speed of cooling, where was that melt created, and where is the evidence of the melting in the sidewalls to the razor sharp fractures from which it has injected into the sidewall?
Are there studies that unequivocally support the concept that a rupture propagates in the way as illustrated in the cartoon provided here? I am not sure. The problem comes down to the use of a principle loosely described as assuming a stochastic interdependence of space and time. Boiled down into a nutshell this principle asserts that the temporal evolution of a phenomenon (e.g. glacial valleys) can be worked out by observing the spatial variation of that same phenomenon, classifying the observed sequence in terms of rank order in terms of the stage of development, and then asserting that this same sequence is the temporal sequence by which this phenomenon progresses.
The method works to some degree, but in many aspects, it fails. The observed spatial variation is often the envelope of the paths taken through time, and it is often not true that the path taken through time must move along the envelope of the observed collection. In other words, as so often assumed in geology, time and space are not interchangeable, and this founding principle has been shown to fail on many an occasion. So is the case with trying to map the temporal evolution of a fault rupture by observing the envelope of fault products.
A rupture propagates quickly whereas it takes time for the movement to take place that generates the fault products. And many large faults have knife-sharp rupture planes when observed in outcrop, with clear evidence that the observed rupture cut through its own brecciation products?
So what are these observations telling us? That there are multiple brecciation episodes with late movement slicing on multiple ruptures. Certainly this is a model supported by the observations in doi:10.26443/seismica.v4i1.1691
A rupture propagates as long as it is driven, which in terms comes down to the lateral extent of the elastic energy stored in the rock mass prior to failure. I imagine that how the Earth works (and yes, I have been influenced by Per Bak) is to self-organise so that more and more energy is stored along a fault prior to its rupture, with an increasing lateral extent of the rock mass that is just below the critical yield stress that needs to be exceeded before catastrophic failure in its load bearing capacity is initiated. This buildup needs to happen over a long strike distance prior to onset of the earthquake.
Once catastrophic failure takes place locally, a triggering perturbation needs to propagate, if the rest of the strained rock mass is going to join the fray. This propagating perturbation could be the rupture front itself, as pointed out in the thought provoking article presented by Earthquake Insights.
But as suggested by doi:10.26443/seismica.v4i1.1691 super-shear ruptures also start in the far field, way ahead of the rupture front. So what is that about, if it is not caused by fast moving stress perturbations that locally trigger the onset of new ruptures in the far field, in the pre-stressed rock that sits waiting to fail. The thought provoking article presented by Earthquake Insights makes me wonder if the processes involved in creating this self-organised critical behaviour also include brecciation, and some prior movement on the structure that will eventually break.
To this intriguing debate please add doi:10.26443/seismica.v4i1.1691 with their abstract and summary as attached below. This adds yet another dimension to the debate, noting ruptures upon ruptures, and the comment that the total moment magnitude released may have been significantly under-estimated by conventional (point source) methodologies.
Abstract:
A large strike-slip earthquake occurred in central Myanmar on March 28, 2025. The aftershock distribution suggests that the rupture of the main shock propagated mainly to the south. However, a large amplitude phase lasting 20 s, followed by a short-period pulse-like phase, were observed at the stations on the north side of the source, while on the south side, multiple peaks without dominant phases continued for 90 s. Using the potency density tensor inversion method, we explain the ”unusual” waveform signature of the Myanmar earthquake by a multiple, asymmetric bilateral rupture, involving boomerang-like back-rupture propagation and supershear.
Non-technical summary:
On March 28, 2025, a large and devastating earthquake occurred in central Myanmar. We used globally observed seismic records to build the source process model of the large earthquake and reveal how the earthquake rupture evolved along the fault. We find that the earthquake ruptured a fault segment of 400 km length, in 80 s. Within the broad apparent southward fast rupture, the detailed rupture evolution was complex, being characterized by a series of discrete sub-events, involving bi-directional, southward and northward ruptures that migrated at fast speeds, partly faster than the seismic shear waves can travel. These findings are critical for our understanding of earthquake-rupture dynamics and assessing the associated earthquake hazard.
Incredible
I had to watch the video a few times to see the full impact. Initially I was just focussed on the cracks in the concrete.