Monday, May 27, 2013

Historical Meteor Shockwave Events That Destroyed Structures


This blog is Part II of a three part series about possible meteor shock wave damages to structures. Part I is about "Google Earth Photos taken the same day as the Chelyabinsk meteor event on February 15, 2013. This blog (Part II) is about structures that have been destroyed (as a result of meteor events) as reported in news since 1900. Part III will be an analysis the Chelyabinsk Zinc Plant Warehouse collapse. I started out to just blog about the warehouse collapse but I decided to put this event in historical context with other meteor events reported in the news.

Before I start, I should explain some of the terminology. A meteoroid is an object like an asteroid but smaller than 1 meter. A meteor is the visible streak of light seen in the sky made by a meteoroid as it impacts the atmosphere. A meteorite is a fragment of meteoroid that has hit the surface of the Earth. This blog was inspired by the historic meteor event at Chelyabinsk Russia where a substantial industrial building collapsed under the influence of a shock wave. I began to research to see if there were other similar events. I was surprised to find five events with reports of the destruction of houses that were apparently caused by meteors since 1900. In these reports there was an understanding that a meteor was involved, but that somehow a meteorite must have hit the structure, although no meteorites were found with any of these events. In three reports the damage is related to the word meteorite, but no meteorite was found; and in two of the reports the phrase "meteoric stone" or "meteoric shower" is used, but again no meteorite was found. Two of these events were criticized as "meteorite events" and I think appropriately so, and I provide links to these criticisms. Where's the meteorite if these structures were destroyed that way? It is important to realize that when the first 4 events happened there was no scientific understanding about meteor airbursts, so a meteorite was the only possible explanation. Airburst science was not developed until 1950's and early 60's.  I think that these events I list below are all shock wave damage events and these events only make sense if they are interpreted in that way. So I want to make it clear that this is my interpretation of these events. 

Prior to the historical meteor event at Chelyabinsk Russia in February, I think some scientists discounted these accounts of meteor events where houses were destroyed. Maybe they still do. One problem is that in only a single account (where a structure was destroyed) prior to Chelyabinsk were scientists were reported to be involved in the investigation. Because of the event at Chelyabinsk in February and the event at Tunguska in 1908 we have some first hand accounts of the effects of destructive meteor shock waves that represent real events. We also can look at well documented accounts of meteorite impacts with houses and other structures where the meteorite is found. There are lots of these events. Most recently on April 19 a meteorite crashed through the roof of a house in Wolcott Connecticut. That is the third meteorite to penetrate a roof in Connecticut since 1971. The two previous meteorites in Connecticut damaged houses 1.64 miles and eleven years apart. One thing seems clear in these events and is that the damage was light enough so that the house could be quickly repaired and more importantly the meteorite in these cases was fairly easy to find. Halliday, et al. (1985) states that "it is clear that an impact on a building greatly increases the probability of recovery of the meteorite, since only a small percentage of falls will strike buildings, whereas half of the recent recoveries have such involvement." In a couple of instances that I found, the meteorite penetrated the whole house and was found in the crawl space. 


I think if we compare these real meteorite events with the events I list below, we must conclude that they are shock wave events, because the damage is much greater than would be expected from a typical meteorite and yet no meteorite is found.


An important test of a shock wave event is that someone saw a bright meteor and reported a loud bang or a series of bangs that is commonly associated with cannon fire by witnesses in older accounts. Based on that test only 2 or 3 of the 6 events (I list below) where structures are destroyed would pass; an event in Mississippi, Chelyabinsk and maybe the Jakarta event. But as a structural engineer I see a potential public safety issue that I feel we need to look at, so I want to error on the conservative side consider all reports of structures being destroyed that have not been proven to be false. There is another potential problem and that is, prior to 1900 there were unscrupulous newspaper accounts of meteors that were made up to help sell papers. I could not find any evidence of this happening after 1900 so I decided to start the inventory of meteor events at the year 1900.  Scientific papers written on structural damage from meteors has been made by Fessenkov, 1955, La Paz, 1958, Graham et al., 1985 and Yau, K., Weissman, P., & Yeomans, D. (1994) listed 10 reports of structural damage in China from 588 to 1879.

The following is an account in the New York Times of what I think is a shock wave that destroyed a large house in 1900 in Mississippi. This event and the event in Shiraz in southwestern Iran are not included in any lists of historic meteorite events that I have seen. I think they were excluded because if it is stated in the report that no meteorite is found then the event is not relevant. But I could not find where anyone has ever compiled an exclusive list of meteor events where structures were reported as being destroyed. Someday I will expand this list to before 1900 and include hut structures that were knocked down in a separate category. 

METEORITE IN MISSISSIPPI. Visitor from the Heavens Explodes and Wrecks a House. Special to The New York Times. NEW ORLEANS, La., July 12.—The little village of Bellefontaine, in Webster County, Miss., thirty miles in the interior from this place, was the scene last night of the fall of an aerolite, or meteoric stone, which completely wrecked the large storehouse of Hodge & Mabry, and destroyed the stock of goods contained in it. The fall of the aerolite occurred between 9 and 10 o clock, during a perfectly clear moonlight night. The destruction of the building was preceded by the appearance of a ball of fire passing swiftly through the air. It gave off during its passage enough light to greatly increase the light from the moon. As it came near a loud explosion was heard and a shower of fire burst forth from all sides of the blazing mass, having the appearance of hundreds of falling stars. The storehouse was wrecked simultaneously with the explosion. The explosion of the aerolite caused a report like the sound of distant thunder or the roll of far-away cannon. The debris of the house is being cleared away in search of the aerolite... Many cinders of a gray gritty metal appearance have been found in the wreckage.

ANALYSIS of the Bellefontaine Event: This event is listed as a "Meteor Wrong" on the internet, but my research shows that this really happened. This expression is a kind slang term for rocks that look like meteorites, but are not. Because Webster County Mississippi has good genealogical records, I was able to find the full name of one of the store owners and then verify that the event happened from a living granddaughter. The store owner was, George Clark Mabry (1874-1952). This is one of the better meteor air burst descriptions that I have read. If anyone can contribute information about this event or other listed events (below) please contact me.

Here is an account of 5 other events (2 with very limited information) since 1900 where houses and one building have been reported to be destroyed by meteor events:

!  In the publication of the Meteoritical Society (Meteoritics 29, 864-871) 1994 there is this report: Sept. 5, 1907 Hsin-p’ai Wei in Weng-li, China meteorite caused a house to collapse, killing a family; “the whole of Wan Teng-kuei’s family was crushed to death.” ANALYSIS: An event scrutinized by the Meteoritical Society, should be a creditable event. In a paper by Yau, K., Weissman, P., & Yeomans, D. (1994) it is stated "The Wan family probably died from the collapse of the house, rather than from a direct fall of the meteorite."

!  The Straits Times (A Malaya Newspaper) on May 17, 1946 reported: Mexico City, Thurs. –The Government announced today that a meteorite destroyed the hamlet of Santa Ana in Nuevo Leon state of Mexico. Eight people were killed and 26 injured. – Reuter. Also in New York Times 5-17-46 and listed by John Lewis in Rain of Iron and Ice.

!  August 15, 1951 Teheran, Iran near . Sixty two houses were destroyed by a meteoric shower. Twelve people were killed and nineteen injured. In addition 300 livestock animals were killed. The event was reported by Iranian newspapers and the United Press. This event is reported to have been published in the Lowell Sun (Massachusetts) on the next day (p.19) but I have not as of yet seen the archives.

!  An event on April 29, 2010 at 4:30 in the afternoon in Durensawit, East Jakarta according to news reports by the Jakarta Globe was investigated by The Institute of Aeronautics and Space (LAPAN) and the National Police's Ballistics and Metallurgy Center (BMC). The head of the BMC said that tests had ruled out a bomb or a gas-canister explosion and said the object was similar to the one that hit in Bone in South Sulawesi on October 8 2009. "LAPAN ruled out the possibility that the object may have been space debris…" Sri Kaloka Prabotosari estimated the meteorite was 30 centimeters in diameter and had an impact velocity of 10 kps. According to Berita Jakarta, a government web site, Thomas Djamaluddin with LAPAN said "it was not detected by transmitter, possibly because of its small size."  The blast has only left dust with the color of a bit grayish (as translated). The homes of Sunarti, Sudarmojo and Marzuki were damaged in the incident with Sudarmojos house taking the brunt of the impact. It blasted a hole in the second floor of the house, sending furniture falling to the first floor, and tore big holes in walls. No one was home when this happened. ANALYSIS: Getty Images owns twelve high resolution photos of the damage made by Romeo Gacad originally posted on May 4, 2010. Unfortunately these photos have recently been removed from their website. One however, was re-posted at WSJ BLOGS(scroll down 14 images). All the photos appear to be of the same Sudarmojo residence. Photos show the roofing material is completely missing above at least 2 adjoining rooms, most of the wood roof framing is still in place but a few pieces are broken and a few appear to be missing and there are piles of clay tile roofing fragments on the floors. One photo shows a large wood (glass?) frame knocked down inside the house. This area appears to be a very high density living area and it is odd that the damage was limited to only 3 adjacent structures. I looked for photographic evidence for an explosion outside vs inside. I think an inside explosion of this magnitude would have removed significant roof framing and left few, if any, roof tiles inside the structure. Photographic evidence suggests a small air burst above the roof at a low altitude but above the roof, that shattered the roof tiles and knocked them down into the house. Witnesses saw a localized flash at about 4:30 in the afternoon but not a fireball. Investigators shied away from using the expression "shock wave" but compared this event with the larger shock wave event at Sulawesi (6 down in TOP TEN table below) the year before. This was the first event in this list where shock wave science appears to be involved, but the estimated velocity of the impact object is 1.2 km/s slower than the 11.2 km/s the theoretical lower limit of meteors. A blog questioning this event was made by Ian O'Neill.  More on this subject after the following event.

!  February 15, 2013 the Chelyabinsk meteorite was visible in the early morning as a brilliant superbolide that created a series of shock waves that damaged some 7,200 buildings and according to the official Chelyabinsk website, 1613 people were injured in the region and 69 people were hospilized. It also apparently triggered the collapse of about 1050 square meters or 11,300 square feet of roof at the Chelyabinsk Zinc Plant (see part I of this blog series). The building described as a concentrate storage facility was constructed with concrete columns and a precast concrete roof deck. This is the most substantial building ever destroyed by a shock wave. My previous blog and my next blog after this one will provide more details about this building collapse so I have cut this short.


Principles of physics limits the range of velocities of asteroids and meteoroids when they first enter the Earth's atmosphere. The escape velocity of Earth controls the lower limit (personal communication with Gareth Collins) and the full range is between 72 and 11 km/s (161,000 to 25,000 mph). Hills and Goda (1998) state that "asteroids with diameters smaller than 50-100 m that collide with the Earth usually do not hit the ground as a single body; rather they detonate in the atmosphere." A shock wave can be generated when the combined forces on the meteoroid cause it to break apart. A potentially damaging shock wave can be produced when the object is a larger meteoroid or asteroid. John Lewis (1996) states that the density of air roughly doubles for each 5 kilometers of altitude. He also states that "our normal intuition would suggest that the faster a projectile is moving the more deeply it will penetrate it's target. But the exact opposite is true for meteors: the fastest moving meteors produce the highest pressures and are crushed to dust at higher altitude." Because of the high speed of the meteoroid, a pocket of high air pressure in front of the meteoroid is created. When the pressure differential becomes higher than the strength of the meteoroid it breaks apart. When this happens it is sometime called a bolide or an airburst. The shock wave energy released is dissipated with distance. So a shock wave that begins high in the atmosphere loses most of it energy by the time it get to the ground. But at the same time it distributes the energy over a larger area on the ground. These events often have sound effects that can be heard. The larger events rattle windows and the even larger events break windows. On July 23, 2001 a bolide meteor shattered windows in towns west of Williamsport Pennsylvania (see Meteorites Don't Pop Corn).  In the reports I have reviewed (above), we might consider that the smallest meteoroid capable of destroying a structure to be roughly about 30 centimeters in diameter (Jakarta event). However, there is a nifty online "Earth Impact" tool to compute the effects of different size meteoroids with different masses, traveling at different speeds and traveling at different angles. This tool created by Collins, Melosh and Markus, makes assumptions and approximations that limit the accuracy of the result particularly for smaller objects. To get more accurate results full computer simulations must be run. So for what it's worth, I used this program to see what the smallest meteoroid was that would produce a damaging shock wave. I went through numerous iterations  and I found the following object:

1.5 meters (4 feet 11 inches) in diameter, a density of 7907 kg/m3 impact velocity of 11.2 km/s, and an impact angle of 85 degrees. The resulting meteor burst occurred at a height of only 170 meters (559 feet) with an energy of .21 kilotons producing a peak overpressure of 17.4 psi at ground zero. The overpressure drops to 3.7 psi at .5 kilometers from ground zero. This event if it were to happen would be very serious, but over a fairly small area. All wood framed structures would be destroyed over an area of about 2 square miles or (5.4 square km). However, there are two versions the impact tool and the new version computes different results without an airburst for the same inputs. So one or maybe both tools have an error. So a mini-shock wave event like this may not be real when you include all the physics. But the original tool indicates that the object needs to impact at the low end of possible velocities and needs to be strong and have a density close to that of an iron meteorite. These factors allow the meteoroid penetrate deeper in the atmosphere before it explodes. The Chelyabinsk meteor by comparison was an object estimated to be 17-20 meters (55.8-65.6 feet) and hit at an angle just under 20 degrees and was initially traveling at about 30 km/s (67,100 mph). It only had a 10% meteoric iron content and it slowed to 18.6 km/s (41,600 mph) when it burst at a height of 23.3 km (14.5 miles).

A list of air burst events have been listed on the internet at: en.wikipedia.org. I have reproduced this table showing only the top ten events and sorted them according to the average estimated yield. By doing that the Chelyabinsk event shows to be #3 and it has widely been reported as being #2. The problem is that there is a very wide range of estimates for the Curuçá River event. A Tunguska type event is believed to occur once every 1000 years and events like Sikhote-Alin occur every 2 years some where on Earth.

                                   TOP TEN SHOCK WAVE EVENTS
EVENT
          DATE
           YIELD (kiloton's)
        AVG.YIELD
Tunguska
6/30/1908
10,000-15,000
12,500
Curuçá River
8/13/1930
100-5,000
2,550
Chelyabinsk
2/15/2013
500
500
Offshore, S Africa
8/3/1963
176-356
266
Arroyomolinos de Leon
12/8/1932
190
190
Sulawesi Indonesia
10/8/2009
31-50
40
Eastern Mediterranean
6/6/2002
12-20
16
Queen Maud Land
9/4/2004
12
12
Marshall Islands
2/1/1994
11
11
Sikhote-Alin, Russia
2/12/1947
10
10















By studying the videos and pictures in the area of Chelyabinsk we can see the effects of shock wave damage. The exterior of a structure that protects it from wind and rain from a structural perspective is called the envelope. Once the envelope is damaged (from doors blown open or by windows blown out) by a shock wave, pressure changes occur inside the building. Interior doors can then be blown open and drop ceilings can be damaged by the pressure changes. Once the envelope is compromised, flexible walls, ceilings or floors can act like a membrane and bounce under the impact of a shock wave. This matches the description of the energy of the impact at Jakarta.

SUMMARY

The following is a summary of the events listed above that I think are shock wave events that mostly occurred before the science was developed:

                                     POSSIBLE SHOCK WAVE
            EVENTS SINCE 1900 THAT DESTROYED STRUCTURES



NUMBER OF
EVENT
DATE
FATALITIES
STRUCTURES



DESTROYED
Bellefontaine Mississippi
7/12/1900
0
1
Hsin-p’ai Wei, China
9/5/1907
a family
1
Santa Ana, Mexico
5/17/1946
8
 a hamlet
Shiraz, Iran
8/15/1951
12
62
Jakarta, Indonesia
4/29/2010
0
1
Chelyabinsk, Russia
2/15/2013
0
1


We don't know the number of structures destroyed in the 1946 event and we don’t know the number of people killed in the 1907 event. But if we add all the occurrences together, we get a total of 6 events since 1900 with an average occurrence of a meteor with a shock wave that destroys at least one structure every 19 years. In 67% of these events only a single structure was destroyed but in the remainder maybe 3 to 62 houses were destroyed. On average about 11 to 15 structures will be destroyed by the event, and the fatality rate per event (when structures are destroyed) is 4 to 5. We can compare these possible shock wave events with known damage from meteorites. Halliday et al. (1985) estimated that 16 buildings per year could receive some damage from meteorites that weigh at least 500 grams (1.1 pounds). Adjusted to the population of Earth in 2013 this becomes 23 buildings per year damaged by meteorite impacts. They used a 20 year period in North America as a sample interval.

The fatality rate from meteors in general is a little higher because only events destroying structures were included (above). But if we add in all meteor events since 1900 we get maybe 2 or 3 more fatalities. There are conflicting reports of one or two deaths related to the Tunguska event in 1908 and a male guest was killed in a bridal party in Zvezvan Yugoslavia while riding a carriage in 1929 by a 40 centimeter meteorite according to a New York Times article. If we add up all the fatalities and assume 3 were killed in 1907 we get a total of 24 or 25 deaths since 1900 with one person killed every 4 ½ years on average. Every one of these fatalities except maybe the one in Yugoslavia I think are the result of shock waves and not being struck by a meteorite. But the occurrence rate of destroyed structures and fatalities must be related to the population of Earth that is now over 4 times as high was it was in 1900. Also note that in the Mississippi, Chelyabinsk and Jakarta events no one was killed, but probably because there was no one in the structures when the shock wave hit. Yau et al., 1994 used data from China to compute that a fatal incident will occur somewhere on Earth every 3 ½ years, adjusted for Earths population change that would be an incident every 2.8 years today. For comparison I find 5 incidents world wide since 1900 where someone was killed that is an average of once every 22.5 years. If I normalize that for a 4x population increase, we might predict an incident with at least one fatality every 9 years.

CONCLUSIONS

I have reviewed 5 events of destruction to residence type structures reported to be caused by meteorites or "a meteoric shower". However, these are all "missing meteorite" stories where the damage is much heavier than would be expected from a meteorite. I interpret these events as shock wave or air burst events. It is important to realize that the first four events happened before the science of meteor shock waves was developed so there was no chance for these events to be correctly understood when they happened. They also predate the sensor grid. The Chelyabinsk meteor event is the first event in history where a structure was destroyed and there is an official meteorite associated with the general event.  And it appears that the damage here was not caused by a meteorite object, but by a shock wave. The Jakarta Event just 3 years ago was not picked up by by the world wide grid of sensors. From personal communication with Peter Brown, University of Western Ontario; he would not rule out this as a shock wave event but added "I think it is unlikely that an airburst capable of producing significant overpressures at ground level would go unrecorded over land (or even the ocean). There are some 20 photos and several newscasts on Utube of this event and I interpret this event as a small, low altitude, airburst mainly because roof tiles were shattered and knocked down into the house. On average 23 buildings per year could be damaged by meteorites but none are destroyed. Meteorites maybe could destroy structures, but the occurrence rate must be considerably larger than 20 year study period used by Halliday et al. (1985) and larger than the 113 year study period I used.

I think all of the meteor related fatalities since 1900 except one, were caused by shock wave events and that most of these deaths are related to the collapse of a structure. It appears that only the fatalities at Tunguska and Zvezvan, Yugoslavia were not related to a structural collapse. It is possible that some of these shock wave events were large events that created limited damage because they occurred in sparsely populated areas. 

On average 23 buildings per year are damaged by meteorites but none are probably destroyed. However, shockwave events that destroy at least one structure appear to occur once every 19 years. The average fatality rate from all meteor events since 1900 is one every 4 1/2 years with only one attributed to a meteorite.


In the future structural damage events (like the ones discussed here) where no meteorite is connected with the damage, needs to be studied by engineers that understand blast damage. A damage map should be made that shows blast displacements. This helps us to understand the forces at work and ultimately the energy of the blast. The specific science that addresses this kind of damage is called structural dynamics. The key evidence is that a meteor shock wave will create a higher overpressure outside the structure and thus weaker parts of the structure (like doors and windows) will be knocked inward. It is also essential to collect witness reports that include descriptions of the sounds, the track of the object, vibrations, damage and location of the observer. There are online forms to report witness information at the International Meteor Organization, the Canadian Space Agency's Meteorite and Impacts Advisory Committee, and the American Meteor Society. I  also see the benifit of mapping glass breakage events because that it a direct result of the energy released. Also did the glass just break or was it knocked out of the frame like we saw at Chelyabinsk?

These reports since 1900 indicate that a shock wave event will destroy one or more structures once every 19 years or so. If these events are real, the greatest danger to human life and to the structures we build, come from shock wave events and not meteorites. Also these events must result from objects smaller than the one that hiChelyabinsk because objects that size hit Earth about once every 90 years. Depending on the structure, the event must produce an overpressure at ground level of 3-4 psi for a structure to be destroyed.

REFERENCES

1. BROWN, P., SPALDING, R.E., REVELLE, D.O., TAGLIAFERRI, E., &WORDEN, S.P. (2000). The flux of small near-Earth objects colliding with the Earth. Nature. 403:165-166. doi:10.1038/35003128

2. COLLINS, G.S., MELOSH, H.J., AND MARCUS, R.A.,(2005). Earth Impact Effects Program: A Web-based computer program for calculating the regional environmental consequences of a meteoroid impact on Earth. Meteoritics & Planetary Science 40, Nr 6, 817–840.

3. HALLIDAY, A. T. BLACKWELL, and A. A. GRIFFIN. (1985). Meteorite impacts on humans and on buildings. Nature. 318: 317. doi:10.1038/318317a0

4. HILLS, J.G. & GODA, P. (1998). Damage from the impacts of small asteroids. Planet Space Sci. 46, 21-19-229.

5. LEWIS, JOHN (1996). Rain of Iron and Ice. Helix Books. 236. ISBN 0-201-48950-3

6. SCHIERMEIR, QUIRIN. (2013). The death of the Chebarkul Meteor. Nature. doi: 10.1038/495016a

7. SPRATT, CHRISTOPHER. (1991). Possible Hazards of Meteorite Falls. Roy. Astr. Soc. Canada, 85, 263-280.

8. Yau, K. Weissman, P. and Yeomens, D. (1994) Meteorite falls in China and some related human casualty events. Meteoritics 29, 864-871.