Mag 6.2 Earthquake near Norcia, Umbria, Italy

[Astronuc]

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

The U.S. Geological Survey said it was a 6.2 magnitude quake that hit near the town of Norcia, in the region of Umbria, at 3.36 a.m. (0136 GMT).

The mayor of the small town of Amatrice reported extensive damage. "Half the town is gone," Sergio Pirozzi told RAI state television. "There are people under the rubble... There's been a landslide and a bridge might collapse."

https://www.yahoo.com/news/magnitude-6-4-quake-hits-italy-near-perugia-015222205.html

There were a number of aftershocks in the region.

 

[Bystander]

Thirty-seven and counting.

 

[Fewmet]

For anyone who does not know about the https://www2.usgs.gov/faq/?q=taxonomy/term/9837 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.

 

[Astronuc]

There was a 5.5 mag earthquake within 4 km or Norcia.
http://earthquake.usgs.gov/earthquakes/eventpage/us10006g7w#executive

And a host of Mag 4-5 in the region - NE Lazio and E Umbria.

 

[Astronuc]

https://www.yahoo.com/news/ap-explains-difference-between-shallow-deep-earthquakes-203009309.html
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.

 

[Fewmet]

https://www.yahoo.com/news/ap-explains-difference-between-shallow-deep-earthquakes-203009309.html
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, were deeper, ~84 km, so the damage to surface structures was not so great. There was damage though.

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.

 

[davenn]

above the Norica epicenter than above the Chauk epicenter.

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

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.

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

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.

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 areaDave

 

[Fewmet]

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

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?

 

[davenn]

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.

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

Can you explain why horizontal motion is more damaging?

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

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

 

[Fewmet]

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

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.

 

[Astronuc]

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

 

[CapnGranite]

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.

 

[1oldman2]

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.
"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.

 

[davenn]

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

Dave

 

[Astronuc]

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.

 

[1oldman2]

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.)

 

[CapnGranite]

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.

 

[davenn]

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.

"from the horses mouth"...

Tectonic Summary
The October 30, 2016 M 6.6 earthquake north of Norcia, Italy, occurred as the result of shallow normal faulting on a NW-SE oriented fault in the Central Apennines. The Apennines is a mountain range that runs from the Gulf of Taranto in the south to the southern edge of the Po basin in northern Italy. Geologically, the Apennines is largely an accretionary wedge formed as a consequence of subduction. This region is tectonically and geologically complex, involving subduction of the Adria micro-plate beneath Eurasia and the Apennines from east to west, continental collision between the Eurasia and Nubia (Africa) plates building the Alpine mountain belt further to the north, and the opening of the Tyrrhenian basin to the west (the latter of which is in turn related to Adria subduction and eastward trench migration). The evolution of this system has caused the expression of all different tectonic styles acting at the same time in a broad region surrounding Italy and the central Mediterranean. The October 30, 2016 normal faulting earthquake is an intraplate event, an expression of the east-west extensional tectonics that now dominate along the Apennine belt.

my boldMoment tensor info ...
http://earthquake.usgs.gov/earthquakes/eventpage/us1000731j#moment-tensor

 

[1oldman2]

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.

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)

http://Earth'sky.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.

 

[CapnGranite]

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

 

[CapnGranite]

Extensional basins in the tectonically bimodal central Apennines fold-thrust belt, Italy: Response to corner flow above a subducting slab in retrograde motion
GEOLOGY, October 1999

Geodynamically induced variations in the emission of CO2 gas at San Faustino (Central Apennines, Italy)
Geofluids (2011) doi: 10.1111/j.1468-8123.2011.00345.x

Graviquakes in Italy
Tectonophysics 656 (2015) 202–214

Continental delamination and mantle dynamics drive topography, extension and fluid discharge in the Apennines
GEOLOGY, June 2013; v. 41; no. 6; p. 715–718;

Contrasting strike-slip motions on thrust and normal faults:
Implications for space-geodetic monitoring of surface deformation
GEOLOGY, March 2013; v. 41; no. 3

Normal fault earthquakes or
graviquakes
Scientific RepoRts | 5:12110 | DOi: 10.1038/srep12110 1

Thermal decomposition along natural carbonate faults during earthquakes
GEOLOGY, August 2013; v. 41; no. 8; p. 927–930

 

[CapnGranite]

Branner Earth Science Library computer responded to my search request and just sent me a list of 274 papers written since 2000 related to the "central Apennines geodynamics", the "L'Aquila earthquake", and ""high pressure carbonate fluids in central Italy". So far, the abstracts don't provide enough insight to merit posting links to locked journal papers. If I find open-access papers or interesting abstracts, I'll post those.

 

[Astronuc]

Drone footage shows devastating aftermath of Italy earthquake
https://www.yahoo.com/news/drone-footage-shows-devastating-aftermath-201359792.html

In Amatrice, the nearly 600-year-old St. Augustine church crumbled on Sunday after surviving previous earthquakes, according to Italy's Vigili del Fuoco (literally "Firewatchers" in Italian).

The church's rooftop sustained damage last week, but the building was still standing as of Oct. 28.

6.6-Magnitude Earthquake Flattens Much Of Historic Basilica In Central Italy
http://www.npr.org/sections/thetwo-...s-much-of-historic-basilica-in-central-Italy/

https://www.yahoo.com/news/italy-hit-strongest-quake-35-years-no-deaths-123915061.html

Italian earthquakes could go on for weeks in domino effect: scientist
https://www.yahoo.com/news/italian-earthquakes-could-weeks-domino-effect-scientist-142116297.html

Gianluca Valensise, a seismologist at Italy's National Institute for Geophysics and Vulcanology, told Reuters there was a "geodynamic link" between the deadly August earthquake and all those that have followed.

Italy's Apennine mountains that run from the Liguria region in the northwest to the southern island of Sicily are dominated by a chain of faults in the Earth's crust, each one averaging about 10-20 kilometers in length.

"An earthquake measuring 6 or larger creates stresses that are redistributed across adjacent faults and can cause them to rupture, and this is probably what we have seen since August," Valensise said.