Posts in the category »  Opinion «  ( 123 Posts )

  • How common are fault re-ruptures?

    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 1: map of onshore and offshore earthquakes (M > 6, z < 30 km) occurred since 2016. Data source: USGS catalogue.

    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.

    Figure 2: a) distribution of the onshore earthquakes, bin size 0,2 magnitude units; b) probability of surface rupture as a function of magnitude.

    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 😊

     

     

     

  • Soft-sediment deformations buried beneath the center of the Dead Sea record hundreds of large earthquakes spanning the past 220,000 years

    1. Key points

    This is the first attempt to apply a computational fluid dynamic modeling-based quantitative “fossil seismograph” to develop a large earthquake record.

    The record is calibrated to historic earthquakes, for which the Dead Sea area has a famously long span, and it confirms a clustered earthquake recurrence pattern and a group-fault temporal clustering model.

    The record yields much shorter mean recurrence for large (≤ 1.4 kyr vs. 7-11 kyr) and moderate (≤ 500 yr vs. 1600 yr) earthquakes than previously obtained, thus reveals a much higher seismic hazard than previously appreciated on this slow-slipping plate boundary.

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  • My top ten list of earthquake blogs

    I am running this blog for more than five years now and it is time to acknowledge the other geo-blogs out there that have inspired me. In order to stay updated I follow the Geobulletin, which monitors the geoblogosphere activity. There are numerous amazing blogs out there that are either fun to read or interesting or both, but here I will focus on the ones dealing with earthquakes/tectonics/geomorphology/tsunamis. Here is my personal, subjective, but honest, list of earthquake blogs that I like and read: more

  • A new Nuclear Power Plant near Karachi

    Karachi is the most populated city in Pakistan with around 24,000,000 inhabitants – just as many as Australia. Since many years a nuclear power plant (NPP) is located just a few miles outside the city at the shore. Ongoing work on new reactors with Chinese help has recently sparked outrage and media coverage. Concerns are that any accidents at the NPP might have dramatic consequences and threaten millions of people. I searched the recent scientific literature on seismic and tsunami hazard for Karachi…

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  • World Heritage Site unacceptably damaged: Nazca Lines, Peru

    Never, never, never ever, for no reason it is justifiable to damage a cultural heritage site. Not in Peru, not anywhere else in the world. Never. It should be always one of our primary objectives to sustain cultural and natural heritage sites. No discussion.

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  • Earthquake in Pakistan – lessons to learn

    After the strong earthquake in Pakistan a good part of the media coverage was about the fascinating story of the new island that emerged off Gwadar. While this was really amazing I think now it’s time to think about the consequences of the quake itself. We have seen a shallow M7.7 event that produced severe shaking across a large area. Peak ground acceleration exceeded 1 g in the 0.3 s period and was still intense in longer periods. 515 people have reportedly been killed and more than 100,000 are homeless. more

  • A mud volcano as an Earthquake Environmental Effect?

    On 24 September a shallow M7.7 earthquake rattled Pakistan. At least 300 people died and thousands of houses, most of them adobe, collapsed in Balochistan Province. The quake was felt as far away as Muscat (Oman) and New Delhi (India). Epicentral intensities reached up to IX. The earthquake appeared to be a strike slip event. Soon the media reported on an amazing effect of the quake – in roughly 400 km distance a new island appeared few hundred meters off Gwadar. more

  • QGIS 2.0 released – watch out ESRI!

    Working on spatial data is the key feature of being a geoscientist and a lot of this work is done using ArcGIS from ESRI. QGIS was always an alternative especially looking at the costs of a full ESRI license. But when it comes to “making maps” QGIS was always behind ArcGIS in map formatting and export. The map composer was more or less … ugly and not state of the art. more

  • Shaky Ground: Check out the new seismology-fantasy-mystery-science-novel by Sharon Kae Reamer

    Shaky Ground is the new novel in Sharon Kae Reamers Schattenreich series. You’ve probably read Primary Fault, so you’re familiar with seismologist Caitlin and her adventures in Cologne. In this case, you will probably head towards your local book store now or you might be happy to find this Amazon link. If not, check out the story about science, fantasy, and the Cologne “Klüngel” and tell us how you liked it in the comment section! You might know the author not only from her novel, but also from her science... more

  • Has Roger Bilham been deported from India because of his seismic hazard warnings?

    A new story came up recently that sounds like the L’Aquila case, but the other way round. Dr. Roger Bilham from the University of Colorado, a well-known earthquake researcher, was denied entry to India earlier this year. He was on a flight to Bhutan and supposed to change planes in New Delhi when Indian officials sent him back to the plane he just arrived on. Officially, he was accused with having the wrong type of visa. Himself and many colleagues, however, are sure that he was deported because he stated that the seismic hazard in India is underestimated. more