The Aix-en-Provence PATA Days are fast approaching and the meeting programme looks super-exciting! Unfortunately, I’ll not attend the congress, but my soul will be there in poster form – presenting author is 1st year PhD student Marco Pizza and the topic is the likelihood of primary surface faulting.
Some earthquakes produce surface faulting, others do not. Several factors affect the outcome of this dichotomous variable (faulting YES/NO), including magnitude, depth, earthquake kinematic and local lithology. The probability of having surface rupture for a given magnitude is a key ingredient in Fault Displacement Hazard Assessment (FDHA). This probability is derived from empirical datasets and the state of the art is summarized in Figure 1, taken from the recently published IAEA Tecdoc on probabilistic FDHA.
Following an un-systematic post-dinner doomscrolling I’m happy to declare May 2022 as the trenchiest month ever. Here’s some exhibits:
Safety first; if cozy and comfy it’s better.
The award goes to Stéphane Baize (@Stef_EQ_Geology) and their trenches along the Cévennes fault: look at the details in the photo… like “paleo” engraved in the wooden frame to prevent collapse of the trench wall. And what about the tent? 10/10 professional style.
Landscape photography award
The winner is Colca Canyon in Southern Peru, take a look at the pictures by Anderson Palomino (@AndersonRPT1) and Carlos Benavente (@clbenavente)
Best flower structure award
No doubts here, easy win for Ian Pierce (@neotectonic) and their trenches in Azerbaijan. Follow him for stunning field photos and videos.
Mention goes to Jade Humprey (@ForFaultsSake).
The tricks of the trade.
Learn them from Jonathan Obrist-Farner (@guateologist) uncovering the mysteries of the 1976 Motagua rupture in Guatemala
Category “You don’t need a trench to find good stratigraphy”.
Prize goes to Gabriel Easton Vargas (@geastonvargas) and paleotsunami research in semiarid Chile
Category “Let’s the student do the work”.
Terrific exhibit by Shreya Arora (@shryaarora) trenching in the Himalaya region
Never without a nijiri gama.
Award is won by Sambit Prasanajit (@SPrasanajit) and their sites in S. Korea
The winner is PhD student Argelia Silva Fragoso (@Argy_sf) from Insubria university, digging trenches in Central Italy
Sorry if I missed someone, I wish you all a safe and fruitful field season!
Five years ago, on October 30, 2016, a Mw 6.5 earthquake nucleated along the Vettore Fault in Central Italy.
This event is particularly interesting because its surface rupture overprinted the faulting occurred only 3 months earlier, on August 24. In the last 5 years, at least 2 other cases of repeated rupture in a short time interval were observed, i.e., the 2016 Kumamoto (Japan) and 2019 Ridgecrest (US) sequences.
Fault re-ruptures are currently not accounted for in seismic hazard assessment; should paleoseismology folks care about re-ruptures? To answer this question, it is necessary to understand how common re-ruptures are.
So, I checked the USGS catalogue, looking for earthquakes with M > 6, depth < 30 km occurred since January 1st, 2016. I chose these thresholds because I’m interested in surface-rupturing events, but maybe the values need some fine-tuning. The search returns 490 earthquakes. Then, I filter out events with epicenters offshore, since surface faulting is more difficult to document there. A total of 104 earthquakes (21% of the total) occurred onshore (Figure 1).
Figure 2a shows the distribution of the 104 earthquakes according to magnitude (bin size 0,2 magnitude units). Now I calculate the expected number of surface-rupturing events, using the probability curves provided by Youngs et al. (2003; their Equation 4) and shown in Figure 2b. Out of the 104 earthquakes, it can be expected that 63 should have produced surface faulting.
Finally, let’s check how many re-ruptures have been actually observed: as mentioned earlier, they are at least Kumamoto, Ridgecrest and Central Italy. Three out of 63 means that ca. 5% of the shallow M > 6 earthquakes onshore include the repeated rupture of the same fault strand(s).
This has strong implications for paleoseismology, because it is virtually impossible to identify events occurring few months or years apart. In turn, this may affect the computation of key parameters for seismic hazard assessment, such as recurrence interval, slip per event and elapsed time.
These ideas are at the core of a project I’m writing right now, called REDEFINE: “RE” stands for re-rupture and Task 1.1.3 will be the update of the probability curves of Figure 2b – no more spoiler on the project!
If I’ll get that 1 million €, you’ll hear more on re-ruptures from me 😊
While working on my project on distributed faulting, I dig into the literature looking for additional case studies beside those contained in the SURE (SUrface Ruptures due to Earthquakes) database.
I retrieved information on 18 normal and strike-slip events occurred between 1905 and 2011, with a magnitude range of Mw 5.9 – 8.3. I digitized rupture traces from published maps at a variable scale, dependent on the resolution of the original map. Earthquakes are from Iran (7 events), Mongolia, China, Turkey, Greece (2 events for each country), Italy, Kenya and Japan (1 event).
The recent publication of a paper on the Weitin Thrust (Papua New Guinea) by Chen, Milliner and Avouac (Fig. 1) gave me the opportunity to dig out and look back to some notes I wrote few months ago. Chen et al. use optical image correlation to document coseismic surface ruptures along the Weitin Thrust occurred in a Mw 8.0 event in 2000 and in a Mw 7.7 event in 2019. The ruptures overlap along a 20-km long portion, with 3-4 m of slip (Fig. 2).
strong earthquakes commonly produce secondary effects (landslides,
liquefaction, tsunamis), which worsen the impact of the seismic event, both during
the emergency and recovery phases.
can be triggered by events of M above 5 or so, and stronger events can produce
thousands of landslides. Landslide inventories were compiled for dozens of
events and the relations between Mw and maximum distance or area affected by
landslides have been analyzed (e.g., Keefer, 1984; Rodriguez et al., 1999). On
the other hand, the total area affected by landslides is one of the metrics
used to assign the ESI intensity (Environmental Seismic Intensity; Michetti et
On July 4th and 5th, 2019 two earthquakes (Mw 6.4 and Mw 7.1, respectively) occurred in eastern California and produced distinct surface ruptures. Field surveys started immediately after the first event and, less than two weeks later, a provisional map of surface rupture was compiled and made available to everyone (Contributors from USGS, CGS, UNR, USC, CSUF). I downloaded the map and kmz files of the ruptures from the SCEC response site, which contains tons of fruitful information.
The two strike-slip earthquakes ruptured two perpendicular faults, the first running NE-SW with left-lateral slip and the second running NW-SE with right-lateral slip (Figure 1). The location of the earthquake falls within the Eastern California shear zone, a region of distributed faulting associated with motion across the Pacific-North America plate boundary, and an area of high seismic hazard.
with a variable degree of complexity: some sectors show a “simple” single
strand, others show multiple sub-parallel or diverging splays. Distributed
faulting represents displacements occurred off the principal fault and is
generally made up by less continuous ruptures, which can be located tens of
meters to a few kilometers from the principal fault trace. A method to evaluate
the fault displacement hazard has been proposed by Youngs et al. (2003) and
later refined by Petersen et al. (2011); the former study analyzed normal
faults, while the latter analyzed strike-slip faults.
the method defines the conditional probability of faulting occurrence as a
function of distance from the principal fault and derives scaling relations
between rupture probability and distance. I applied the same method on the 2019
sequence and compared the output with the results by Petersen; results are
grid-dependent – since available data are still provisional, I used a quite
coarse grid size of 200 m, more detailed studies will come.
Results are in good agreement (Figure 2): the 2019 ruptures show a higher than average rupture probability at 0-2 km from the main fault, but also taper out faster than the previous events.
D., et al. (2011). Fault displacement hazard for strike-slip faults. BSSA,
R., et al. (2003). A methodology for probabilistic fault displacement hazard
analysis (PFDHA). Earthquake Spectra, 19(1), 191-219.
On Thursday 28th June, I had the opportunity, together with over 40 students and Early Career Researchers, to attend the full-day summer school organized during the 9th PATA Days Congress in Possidi, Greece.
Gotha speakers gave short lectures on a variety of topics; well, it’s quite strange realizing that behind a book cover or a long list of papers you’ve read there’s a real person with a face, 2 hands and 2 eyes… but that’s what happened to me.
Location, location, location
As geoscientists, we all know the importance of a proper location… the Possidi Holiday Resort is just 20 m from the beach! Even the storm Hera did not prevent us to go for a swim.
The Possidi Beach. Photo by Sofia Christoforidou.
The summer school
The first lecturer was Klaus Reicherter, dealing with tsunamis in the Mediterranean and in Greece and highlighting the inherently multidisciplinary nature of such a research.
Tom Rockwell focused on strike-slip fault with worldwide examples – S. Andreas, North Anatolian, Great Sumatra and Dead Sea Faults – and field-based results.
Jim McCalpin spoke about the use of paleoseismology in seismic hazard assessment, giving us a bucket of real-life examples, experiences, good (and less good) practices. And I learned that when building a logic tree, a 5% probability is not denied to (almost) everybody.
Shmulik Marco showed on- and off-fault archaeoseismological evidences and soft-sediment deformations along the Dead Sea Fault. Plus (in my opinion) the best tip of the day: keep good relations with archaeologists, you never know what they will discover under the dirt.
Then, Spyros Pavlides dealt with active faulting in multi-fractured seismic areas, and specifically the Aegean region. Just in case you are wondering if there’s something simple there, ehm… no, you should consider multiple tectonic phases, inherited structures, the presence of normal faulting, subduction zones and volcanic activity all together.
We definitely changed perspective with Manuel Sintubin, speaking about earthquake risk communication and the need to move from a risk message model toward a risk dialogue model; this is a super-important topic not always addressed in the proper way, with possible huge consequences.
Ioannis Papanikolaou spoke about the seismic landscape, extraction of slip rates and fault specific SHA with tens of examples from Greece and Italy and useful tips on advantages and disadvantages of each methodological approach.
Finally, Georgios Syrides gave a lecture on sea level change indicators. Well, I’m very ignorant on this because simply it’s not my bag, so I learned lots of things (bonus: super-cool photos!).
Here’s the PATA team! (yes, I’m quite mad with football and the World Cup was ongoing…)
“He who knows only his own side of the case knows little of that” – John Stuart Mill, On Liberty, 1859
I saw top scientists jump on their seats when other top scientists called “small” a M 6 or “moderate” a M > 7 earthquake. Or when a trench revealing 5 events was called a “short record”. We all have different perspectives, opinions and experiences. And with “we” I mean all of us, from top scientists down to undergraduate students. I think it’s a richness and we should take care of it.
Final remarks: thanks!
The success of the summer school and the whole 9th PATA Days meeting would not have been possible without the contribution and efforts of the Thessaloniki University staff. A big thank to all of you and see you in the next PATA meeting!
Surface faulting is commonly observed after moderate to strong (Mw > 6.0) earthquakes. Beside primary faulting along the seismogenic structure, distributed faulting (DF) may occur in the vicinity of the principal faulting (ANSI/ANS-2.30, 2015). DF may impact wide areas and its forecasting is particularly relevant for the design of critical or distributive infrastructures (e.g., nuclear power plants). DF assessment is currently pursued through probabilistic fault displacement hazard assessment (PFDHA): in this approach, the conditional probability of DF occurrence is computed as a function of magnitude and distance from the primary fault. Empirical regressions were obtained for the different tectonic styles, based on a limited number of case histories (e.g., Youngs et al., 2003 for normal faults). more
Paleoseismicity.org is a page dedicated to scientists and everyone else interested in paleoseismology, archeoseismology, neotectonics, earthquake archeology, earthquake engineering and related topics. Different authors irregularly write about recent papers, field work, problems, conferences or just interesting things that they come across. We intend to provide a platform for discussion and scientific exchange. Interested in joining as an author? Please contact us!