Posts in the category »  Earthquake «  ( 123 Posts )

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 😊

The Bulletin of the Geological Society of Greece (BGSG) is inviting papers for a Special Issue on the 2021 Northern Thessaly, Greece, Earthquake Sequence. This sequence included a M6.3 mainshock on March 3, followed 32 hours later by a M6.0 event and a M5.6 event on March 12, and thousands of smaller aftershocks. This was the most significant earthquake sequence in northern Thessaly in 80 years, and the first large events in this area of Greece since the major upgrades of the seismological, strong motion and geodetic networks. Remote-sensing imagery is available from a number of satellites and other platforms. The sequence raises numerous questions related to fault interactions, blind faulting, near- and far-field ground motions, damage distribution, earthquake triggering, liquefaction phenomena and seismic hazard and seismotectonics of the Northern Thessaly.

The March, 2021 earthquake series in Greece ruptured a previously unmapped fault and caused severe damage in the epicentral area. The largest shock had a magnitude of M6.3. In this presentation, Athanassios Ganas and colleagues summarize their first observations from space geodesy and field evidence of earthquake environmental effects.

On 3 March, 2021, an earthquake of magnitude M_W6.3 hit northern Thessaly in Greece. According to the USGS, the hypocentre was at 11.5 km depth. Normal faulting occurred either on a plane dipping 55° to the SW or on a plane dipping 36° to the NE. The quake caused a lot of damage in the village of Tyrnavos (Τύρναβος) and the surrounding areas. Widespread liquefaction was also observed. On 4 March, 2021, a mb5.8 aftershock occurred. Our colleagues S. Pavlides, A. Chatzipetros, S. Sboras, E. Kremastas and A. Chatziioannou have prepared a first field report in which they document the environmental effects of the quake.

Following the 2020-12-29 magnitude 6.4 earthquake in Croatia, a late breaking session was accepted by EGU. The session The Dec. 2020 earthquake sequence in Petrinja, Croatia, and its seismotectonic and geodynamic environments will be convened by Stéphane Baize, Sara Amoroso, Lucilla Benedetti, Petra Jamšek Rupnik, Branko Kordić, Snjezana Markušić, and Bruno Pace. The deadline for abstracts is 28 February, 2021. Abstracts need to be send to the conveners by email. You’ll find the email addresses on the session website.

The recognition of sedimentological traces of earthquakes in the form of seismites within Pleistocene sediments is the main objective of the GREBAL project (Recognition of traces left by earthquakes in Pleistocene sediments affected by glacio- isostatic rebound in the Baltic Sea Basin). The investigations focus primarily on Poland, Germany, Latvia, Estonia and Lithuania. Project leader Małgorzata (Gosia) Pisarska-Jamroży has summed up new results from this international research effort.

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 1988 Spitak Earthquake with a magnitude of M_S6.8 took the life of thousands of people and caused widespread devastation in Armenia. It also ruptured the surface and is one of the best-studied seismic events in the entire Caucasus region. 30 years after the catastrophe, an conference will be held in Yerevan, Armenia, from 3-7 December: “30 years after Spitak Earthquake: Experience and Perspectives“. The meeting will also include a field trip to the epicentral area. Full conference fee is USD 200. Download the flyer here (pdf, 655 KB). The form for the expression of interest is here (docx, 19 KB). more

On 21 August an M_D4.0 earthquake hit the Island of Ischia, Italy. The event occurred at a depth of only ~2 km. Despite the low magnitude, the earthquake had dramatic consequences, and two people were killed by collapsing houses. The INGV EMERGEO working group and CNR-IAMC have now published a report on the coseismic effects of this earthquake, which include ground cracks and mass movements. The full report can be found at earthquakegeology.com or downloaded as a pdf here (3.15 MB).

Please cite the report as: EMERGEO Working Group, Nappi et al. (2017). The august 21, 2017 Isola di Ischia (Casamicciola) earthquake: Coseismic effects, doi:10.5281/zenodo.1003188

Report on the International Field Trip “From 1997 to 2016: three destructive earthquakes along the Central Apennine fault system”, 19^th-22^nd July 2017, Italy

Website: http://convegni.unicam.it/TDEq_centralItaly ( including program and abstracts, field trip guidebook and list of participants)

Authors: Chiara Frigerio¹, Alessandro Maria Michetti¹, Francesca Ferrario¹, Franz Livio¹, Emanuele Tondi²

¹Università dell’Insubria, Dipartimento di Scienza ed Alta Tecnologia, Como, Italia

²Università di Camerino, Sezione di Geologia, Scuola di Scienze e Tecnologie, Italia more