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 1^st, 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 😊

This months we have a lot of studies on Mediterranean tectonics, first of all from Italy, and many papers on China and the US. Besides, there are some interesting methodological studies and research from areas that had recent seismic crises such as Puerto Rico and Thessaly. Enjoy reading!

A new Special Issue has just been published in the Journal of South American Earth Sciences: Hazardous Faults in Latin America. The issue contains 16 research papers and an editorial. It was edited by Carlos Costa and Laurence Audin. The issue collects highly interesting contributions from all across the continent. Although subduction megaquakes on the Chilean Trench come with the highest magnitudes, onshore faults pose a significant hazard and historical events have had catastrophic consequences. Also, studying crustal earthquakes and faults is a pre-requisite for understanding crustal deformation, mountain building, and the landscape response to tectonics. Read the Special Issue now, because all papers are free to access via ScienceDirect until 20 Jan 2022.

A new special issue has been published in MDPI’s Geosciences. The collection “New Perspectives in the Definition/Evaluation of Seismic Hazard through Analysis of the Environmental Effects Induced by Earthquakes” collects five review papers, 13 research articles, and an editorial. The SI was edited by Sabina Porfido, Giuliana Alessio, Germana Gaudiosi, and Rosa Nappi. The volume is also available as a book. Download the flyer as a pdf here.

Western Slovenia hosts well-known active strike-slip faults, which accommodate the northward motion of the Adriatic Plate. So far, very little was known about large earthquakes on those faults. This is mainly due to the low slip rates. In a new paper we present geomorphological, geophysical, and paleoseismological data from the Idrija and Predjama Faults, which are among the longest faults in the area. We show that tectonic geomorphology and paleoseismology are really complicated in this kind of geological setting, but we also present data that indicate strong earthquakes during the Holocene. Here’s a short summary of what we did and what we found:

Only one month has gone and the list of new papers is again quite long. We have classic paleoseismology, a number of studies on historical earthquakes, some cool tsunami stuff, and a few more general papers on earthquake geology; plus: an inspiring article by Jim and Eldon on the science and the business of paleoseismology. Enjoy reading!

For most of us the summer break is over and teaching, field work, and office work is starting again or has already started. Time to catch up with the latest papers I suppose! This time we have quite a lot of “classical” paleoseismology in our list, but also plenty of interesting remote sensing and tsunami stuff. Enjoy reading!

In a recently published open access paper in TECTONICS, Zebari et al. report for the first time fault slip rates from Iraqi Kurdistan in the NW Zagros Fold-Thrust Belt. This area is challenging when it comes to narrowing down the distribution of S-N shortening and the associated fault slip rates, because in general, faults don’t reach the surface there. For this reason, we used a proxy: we dated uplifted river terraces with stimulated luminescence and used kinematic modelling of the Zagros fold belt. With this approach we can show that slip rate of the Mountain Front Fault is about 1.5 mm/a. Detachment folds take up another ~1.6 mm/a.

Bad news – the PATA Days in Chile are cancelled. The ongoing Corona crisis does not allow for proper planning and many restrictions are still in place. Visitors to Chile might need to quarantine, air travel might be restricted, and it is not clear when larger gatherings will become possible again. Postponing the PATA Days is not an option, because the preparations for PATA2022 in France are already making progress (update soon!). A huge thanks to the organisers for trying so hard and for all the work they have put into the organisation so far! Great job, team Chile! We hope that one day we can all enjoy your hospitality and the wonderful geology. This is perhaps a good time to watch again the virtual PATA2020 short meeting. Here is the official announcement of the organisers:

Today’s paper list contains a lot of interesting studies on Asian tectonics, a few articles on the Ridgecrest Earthquake, and a number of papers that I was involved in (sorry for the shameless self-promotion). Enjoy reading and let me know if I have missed something.
UPDATE 2021-08-03: Yes, I missed something. I added the last three papers by Rimando & Peace, Kempf & Moernaut, Amey et al., DePaolis et al., & Wils et al.