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Mag 6.2 Earthquake near Norcia, Umbria, Italy

  1. Aug 24, 2016 #1

    Astronuc

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    USGS reports a Mag 6.2 earthquake near Norcia, Italy.
    http://earthquake.usgs.gov/earthquakes/eventpage/us10006g7d#executive
    http://earthquake.usgs.gov/earthquakes/eventpage/us10006g7d#region-info
    https://www.yahoo.com/news/magnitude-6-4-quake-hits-italy-near-perugia-015222205.html

    There were a number of aftershocks in the region.
     
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  3. Aug 24, 2016 #2

    Bystander

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    Thirty-seven and counting.
     
  4. Aug 24, 2016 #3
    For anyone who does not know about the PAGER system, it posts predicted estimates of fatalities and economic impacts for earthquakes of magnitude >5.5, usually within 30 minutes of the event. The estimates are broad, but I value the way PAGER takes into account population density and regional construction material to give a sense of potential impacts. I find the figures for how many people felt what Mercalli magnitudes to give a sense of what it must have been like. Looking at that and other parts of the M6.2 Norica and M6.8 Chauk, Burma PAGERs might be instructive.
     
  5. Aug 24, 2016 #4

    Astronuc

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  6. Aug 25, 2016 #5

    Astronuc

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    https://www.yahoo.com/news/ap-explains-difference-between-shallow-deep-earthquakes-203009309.html [Broken]
    The earthquakes in Italy have been relatively shallow, and consequently, a lot of damage was done to surface structures. In contrast, the 6.8 Mag earthquake near Chauk Burma, was deeper, ~84 km, so the damage to surface structures was not so great. There was damage though.
     
    Last edited by a moderator: May 8, 2017
  7. Aug 25, 2016 #6
    I am more of a historical geologist and geomorphologist than a seismologist, but I think the article in the link provides an explanation of why the ground shook more dramatically above the Norica epicenter than above the Chauk epicenter. Expressed in different terms, the peak horizontal ground acceleration at Norica was measured to be .25g with a maximum horizontal ground speed of 15 cm/s, while at Chauk they were calculated (rather than measured because there are far fewer seismometers in the region) to be about .21g and 10 cm/s.

    It seems pretty clear to me that the number and quality of structures is a more significant factor when talking about how much damage is done. Take the people affected to be a guide to the number of structures. In Norica about 2 million people experienced strong, 234 thousand felt very strong or 13 thousand felt severe shaking. For Chauk the most severe shaking was "strong" and about 1.5 million people felt that.
     
    Last edited by a moderator: May 8, 2017
  8. Aug 26, 2016 #7

    davenn

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    just a small correction for your future reference ... you need to remove the word "above" the 2 times you used it
    the epicentre is the point ON the surface directly above the FOCUS :smile:

    it is a factor, but not the only significant contributing one.

    1) depth of the event is very significant, as distance attenuates ground motion
    2) the type of motion on the fault is also signif. as this determines the type of shaking
    sharp horizontal motion is more likely to damage buildings that vertical motion
    3) ground type also plays a significant part and along with building heights

    these are just a few of the things that need to be considered

    again, the depth is a significant factor here. When comparing 2 events of the same size ( and the Italy and Burma ones were not), the deeper event
    will be felt less strongly over a wider area where the shallower event will be felt more strongly over a smaller area


    Dave
     
  9. Aug 26, 2016 #8
    I am duly embarrassed. Thanks for catching that.

    I am a little surprised that horizontal ground motion is more damaging to building that vertical motion. Reflecting, I think my impression comes from hearing that the 1988 Armenian earthquake was so devastating becasue of poor construction and the strong vertical component of the thrust fault. Can you explain why horizontal motion is more damaging?
     
  10. Aug 26, 2016 #9

    davenn

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    poor construction is a problem of all 3rd world countries and a few slightly more modern ones like Italy and Greece for example
    that have next to zero building codes when it comes to seismic hazard mitigation

    They cannot handle small events, let alone M6+ ones

    have a think about how the building responds to horizontal rather than vertical strong motion

    draw a building and consider what is happening at the base of the building compared to further up at the roof
    and how that is also going to be worse if the building is multi-story

    tell me your thoughts :smile:

    just for your interest, I recorded both the 6.2 Italy and 6.8 Burma quakes here in Sydney, Australia on my seismic system

    D
     
  11. Aug 26, 2016 #10
    I see several considerations. The way you ask the question makes me think you are nudging me toward seeing the net upward force acting on a building is diminished by the weight of the building. That means the magnitude of the building accelerations (and of the change of accelerations during reversal of direction) are smaller that those from similar-sized horizontal motions. This favors lateral motion causing more damage.

    On the other hand, I expect that the lateral ground motion varies more or less sinusoidally, so the reversal in building direction involves a relatively gentle acceleration. For the vertical motions there would be a more rapid acceleration going from down to up than from up to down. My intuition is that would be greater than any lateral accelerations and cause greater damage, but I don’t know the actual values involved and see that could be incorrect.

    Thinking about the structure of the building (and exposing my shaky engineering perspectives) I would think the lateral flexibility would reduce damage due to that direction. I would also think (especially if construction was not done with earthquakes in mind) that the lower floors are already near the “breaking point” and increasing the forces acting there would risk failure of the structure.
     
  12. Oct 26, 2016 #11

    Astronuc

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    Two more earthquakes - on the border of Umbria and Marche

    Earthquakes shake central Italy near devastated quake zone
    http://www.cbsnews.com/news/earthquake-shakes-italy-devastated-quake-zone/

    M5.5 - 8km ESE of Sellano, Italy
    2016-10-26 17:10:37 UTC - 42.857°N 13.023°E 10.0 km depth
    http://earthquake.usgs.gov/earthquakes/eventpage/us20007guy#executive

    M6.1 - 3km W of Visso, Italy
    2016-10-26 19:18:08 UTC - 42.934°N 13.043°E 10.0 km depth
    http://earthquake.usgs.gov/earthquakes/eventpage/us1000725y#executive

    and a number of aftershocks
     
  13. Oct 27, 2016 #12
    Even though the quakes in this part of Italy are along the plate boundary that runs the length of Italy, the central Apennines quakes tend to be shallow and due to extensional dynamics. Rather than being due to subduction, strike-slip, or thrusting, these seems to be mostly on normal faults. More interesting, the area from south of L'Aquila to Perugia---where these quakes are clustered-- is underlain by shallow trapped reservoirs of high-pressure fluids, including CO2. The gas is probably from the mantle and sourced by subduction. There are CO2 vents throughout the area and are also detected during the seismic events. It seems to me that frequent shallow graviquakes are likely as long as there are reservoirs of high=pressure fluids exacerbating, if not directly causing, seismic activity.

    As a side story to the L' Aquila quake of 2009 is the activity of the toads.
    Toads can 'predict earthquakes' and seismic activity
    http://news.bbc.co.uk/earth/hi/earth_news/newsid_8593000/8593396.stm

    http://onlinelibrary.wiley.com/doi/10.1111/j.1469-7998.2010.00700.x/abstract
    Predicting the unpredictable; evidence of pre-seismic anticipatory behaviour in the common toad
    Abstract
    The widespread belief that animals can anticipate earthquakes (EQs) is poorly supported by evidence, most of which consists of anecdotal post hoc recollections and relates to a very short period immediately before such events. In this study, a population of reproductively active common toads Bufo bufo were monitored over a period of 29 days, before, during and after the EQ (on day 10) at L'Aquila, Italy, in April 2009. Although our study site is 74 km from L'Aquila, toads showed a dramatic change in behaviour 5 days before the EQ, abandoning spawning and not resuming normal behaviour until some days after the event. It is unclear what environmental stimuli the toads were responding to so far in advance of the EQ, but reduced toad activity coincides with pre-seismic perturbations in the ionosphere, detected by very low frequency (VLF) radio sounding. We compare the response of toads to the EQ with the reported responses to seismic activity of several other species.

    http://blogs.agu.org/landslideblog/...etect-forthcoming-earthquakes-and-landslides/
    Can toads detect forthcoming earthquakes (and landslides?)

    I wonder if those toads had anything to do with legal woes that seismologists and geologists suffered in courts for the "botched" quake warning.
     
  14. Oct 27, 2016 #13

    1oldman2

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    Concerning, http://blogs.agu.org/landslideblog/...etect-forthcoming-earthquakes-and-landslides/
    I can't help but suspect that the date of disappearance is relevant, no direct correlation, just a hunch.:wink:
    "However, on 1st April, five days before the event, 96% of the male toads disappeared."
    Seriously though, that is a large percentage, i think its likely they did "bug out" but for reasons other than impending Earthquakes.
     
  15. Oct 30, 2016 #14

    davenn

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    Italy getting hammered again
    another quake coming in on my recorder as I type this ... M 6.6 - 6km N of Norcia, Italy
    It's in the same area as the other recent ones

    the red one is the current 6.6, the blue one is the 6.1 of about a week ago

    upload_2016-10-30_18-15-36.png


    Dave
     
  16. Oct 30, 2016 #15

    Astronuc

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    I hope that region is densely instrumented in order to ascertain the reason for the recent surge in activity.

    I'm wondering if there is any uplift in the region.

    I think most parts of the populated world are thoroughly unprepared for very large and destructive earthquakes, or other natural events.
     
  17. Oct 30, 2016 #16

    1oldman2

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    I'm in a D-3 game with a friend near Rome at the moment, he says there is lots of instrumentation in the area of the quake, also heavy damage no deaths reported yet although a lot of structural damage and the area is quarantined. ( It shook Rome area pretty good but no damage reported there, everyone's expecting more shocks soon and no one feels safe about sleeping tonight.)
     
  18. Oct 30, 2016 #17
    I have been wondering about uplift, too. Given that the region is supposedly experiencing overall extensional dynamics, I'd expect a measurable net subsidence using GPS monitoring. To me, uplift would suggest that the high-pressure fluids are moving upward at a higher rate than gravity is allowing the down side of normal faults to drop. It could also mean that the normal faults aren't acting as extensional features, but more as reverse faults and the quakes represent a net upward movement of a "down" block. This is probably why the AGU is strongly suggesting that those of us who don't know much about the area to not post armchair geotheories online.
     
  19. Oct 30, 2016 #18

    davenn

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    "from the horses mouth"................
    my bold


    Moment tensor info ....
    http://earthquake.usgs.gov/earthquakes/eventpage/us1000731j#moment-tensor
     
  20. Oct 30, 2016 #19

    1oldman2

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    Per Dave's USGS link, that's one of the most complex fault zones I've ever heard of. I'm still trying to make sense of the dynamics involved with that area, seems rather convoluted even for the armchair crowd. Myself I'm still reading up and trying to make sense of it.
    Here are a couple of news clips on the event.
    http://www.bbc.com/news/world-europe-37817399
    http://www.bbc.com/news/world-europe-37815188
    A strong earthquake has struck near Norcia in central Italy, destroying numerous buildings.
    The tremors come nearly two months after a major earthquake killed almost 300 people and destroyed several towns.
    Sunday's quake measured magnitude 6.6 and was at a depth of only 1.5km (0.9 miles). (Depth seems at odds with the USGS report) o_O

    http://earthsky.org/earth/6-6-magnitude-earthquake-italy-oct-30-2016
    The U.S. Geological Survey is reporting a 6.6 magnitude earthquake in central Italy this morning (October 30, 2016). There are no deaths or serious injuries reported so far, but several people had to be pulled from rubble. And several buildings have been destroyed, including the Basilica of St. Benedict at the Monastery of St. Benedict in Norcia, Italy. At this writing, there are 11 casualties reported, with aftershocks occurring about every 20 minutes, according to CNN.
     
  21. Oct 30, 2016 #20
    I tend to go to the horse's mouth for the first insights, but then go to the many professional journals. Here is a list of open-access papers on L'Aquila, most of which are relevant to the mid-Apennines as a whole. I have about forty open-access and locked papers on the region as a whole. I'll post those as I open them to see what's in them.

    http://agupubs.onlinelibrary.wiley.com/agu/search/?journal-doi=10.1002%2F%28ISSN%292169-9356&q=L%27Aquila [Broken]
     
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