Tuesday, September 10, 2013

PLANETARY TREMORS: Very Powerful 6.6 Magnitude Quake Strikes Guatemala Causing Panic Among Residents - Many Reports Of Damage And Injuries; Houses Collapse; Landslides Block Highways; Blackout In Some Areas; Quake Felt In Neighboring Countries; The 11th Magnitude 6.0 Or Over Tremor In JUST 8 DAYS!

September 06, 2013 - GUATEMALA - A 6.6-magnitude earthquake shook Guatemala's Pacific coastline on Friday evening, causing some adobe homes to collapse in a town near the epicenter. There were  immediate reports of injuries.



USGS earthquake location - Terrain View.

The U.S. Geological Survey said the epicenter was 6 kilometers (3 miles) south of the small town of Pajapita, near the border with Mexico, and 168 kilometers west of Guatemala City. It had a depth of 67 kilometers (41 miles).

EMSC is giving a magnitude of 6.5 at a depth of 95km. Both calculations show that this was a deep earthquake.



USGS earthquake location - Satellite View.

Guatemala's fire department issued a statement saying some poorly-built homes were destroyed in the town of Patzicia, located between the epicenter and the capital city. The Central American nation's natural disaster agency said that at least three uninhabited homes collapsed, and two highways were blocked by landslides.

Reports of Damage:


1:42 UTC:
-4 homes collapsed in San Miguel Sigüila, Quetzaltenango.
-A house collapsed in the village of San Sebastián Lemoa, Quiché.
-2 women were injured in San Marcos.
-There are damaged houses in Patzicia, Chimaltenango.
-A house caught on fire due to the quake in Tiquisate, Escuintla
-Damage can be seen on the roof of Rafael Landívar University.
-Ceiling fell on the Enriquez passageway in Xela.

1:14 UTC: There are collapsed and heavily damaged houses around Quetzaltenango. Also 1 person has been injured by falling debris in there.

1:08 UTC: Unconfirmed reports indicate that 3 houses, damaged on last years quake, have collapsed with no people inside.

1:03 UTC: People have been injured, most of them from traffic accidents.

12:49 UTC: There are reports of damaged houses as well as collapsed walls around Guatemala. A very big landslide has been reported in kilometer 214.

12:44 UTC: USGS expects that 41,000 people felt  a Very Strong shaking (Mercalli Scale of VII), 1,351,000 a strong shaking (MMI of VI) and almost 4 million people feeling a Moderate shaking (MMI V). If these values are correct then this is a very dangerous earthquake.

12:39 UTC: Damage has been reported in San Marcos, Guatemala. Broken windows have been observed in a municipal building of San Marcos.

12:37 UTC: Power is out in some locations around Guatemala. Landslides could had happened since the area has been hit by hard rains lately.

The quake was felt strongly in the capital of Guatemala City, and caused blackouts in some areas, but authorities did not immediately report any damage there.

"People living in Guatemala City's tall buildings were panicked," said Eddy Sanchez, director of Guatemala's National Institute of Seismology.



USGS earthquake shakemap intensity.


People ran outside their homes and some motorists stopped their cars in the capital. An aftershock of a lower magnitude further frightened capital-dwellers.

Eye-Witness Reports - USGS:


Guatemala City - The house started shaking and it got a little worse but is was only scary for a few seconds.
San Pedro La Laguna - Lasted about 40 seconds. Mild at first, everything stated rumbling when it peaked
Panajachel, Guatemala - I was on the phone with my mother who was calling from Panajachel as it happened, she said it was pretty strong and everyone was running outside.
Guatemala, City - very strong shaking :
Guatemala City - (I'm a pilot staying overnight in Guatemala City at the Crown Plaza by the airport. On the second floor my bed started moving as I watched TV and progressively got worse for about 10 seconds then subsided. A very weak aftershock occurred 5-10 min later. So far no damage can be seen.
Pacoxom - Light fixture swayed, dishes rattled, we exited house.
Quetzaltenango - On second floor of colonial hotel in center a good 30 second shake - quickly exited down stairs and out to the street with a number of other people as it stopped. Some folks were shaken up. Every cell phone was out. As others, felt aftershock about 10 minutes later - maybe 5-10 seconds in duration. And life goes on...
San Pedro La Laguna, Lago Atitlan - Everything was shaking, things fell of the shelf, I ran outside and all my puppies were crying.
Quetzaltenango - very strong shaking small items have fallen,
San Marcos La Laguna - My apartment was shaking very strongly for what felt like a minute or two. Lots of noise as windows and refrigerator and pots/pans shook. Only one small item fell on the floor, and no other visible damage, but the noise and shaking were quite strong.

Eye-Witness Reports - EMSC:


Panajachel - No objects knocked down, but good amount of shaking and seemed to be an aftershock w/in 5-10 minutes.
Guatemala - I felt my knees shake. And I ran out the door.
Antigua / Guatemala - was sitting on the bed with some friends watching a movie when the room began to shake and books fell off the shelves. ran outside and the ground continued to roll for a few seconds. moderate shaking - felt one weaker aftershock so far.
San Cristobal de las casas, Mexico - Started to feel the sway while at my desk. I ran outside and it lasted for what seemed to be about a minute. I am still feeling things settle into place, several minutes later.
Guatemala City - It was horrible.
Santa Cruz la Laguna - A few seconds. Nothing major.
San Jose Chacaya - Moderate shaking but very long... about 15 sec.
San Pedro La Laguna - Ground shook. What else to say?
Quetzaltenango - the quake was strong and long. still feeling aftershocks.
Guatemala City - Yea I was sitting on my bed then felt a little shake and boom it hit
Buena Vista - We have an Academy here and the block walls were waving up and down.
san marcos la laguna solola guatemala - I have a restaurant here in the village centre and the shake took bottles of the shelves.The building shook quiet a lot
Ciudad de Guatemala - stuff shook!
Antigua / Guatemala - the roof started creaking first and then the ground began to move. i got into a reinforced doorway and then the whole house began to roll like on a giant wave. no damage, other than to nerves
Guatemala City - Closet and shower door were moving. It went on about a minute.
Guatemala City - Shaking side to side in my hotel
Santa Cruz la Laguna - I felt shaking for approx. 15 seconds. Not as bad as the one in the fall of 2012, which was 7.2. Slight aftershock.
Antigua - light shaking felt inside and outside. small after tremor
centro dos south of nuva concepcion - Reading a book when it started felt pretty strong nothing broke here just a long period of shaking
Antigua - I was looking up information in Wikipedia on the Island of Garbage in the pacific, and also learning some icelandic when, Bam, here it comes, and I'm like, today is far too hung over a day to die.
Zone 14 Guatemala City - On floor 12 multi axis shaking 90 seconds with several aftershocks. On phone with person across town who also felt it. Strongest felt in 2 years.
Panajachel - The bed and closet units started moving around, floor shaking, lasted about 30 seconds, no damage!
Antigua - My 3 story hotel was rocking...pretty strong.


The temblor was also felt in neighboring Mexico and El Salvador, but there were no immediate reports of injuries or damage in those countries.



Google earthquake location.

Friday's temblor was one of the strongest in Guatemala since a 7.4-magnitude earthquake last November killed 42 people in the country's west. That quake was the strongest in 36 years and left thousands of people homeless and without electricity or water. 

SOURCES: ABC News | Earthquake Report.




Tectonic Summary.
The September 7, 2013 (UTC) Guatemala earthquake (Mw6.6) occurred near the west coast of Guatemala in the Middle American trench. The event occurred at or near the interface between the Cocos and North America plates.   The style of faulting based on the W-phase source mechanism indicates slip likely occurred on a shallow thrust fault consistent with the subduction interface.  At the latitude of this event, the Cocos plate moves towards the north-northeast with respect to the North American plate at a rate of 78 mm/yr.

The broad scale tectonics of the western and southwestern coast of Central America are dominated by the northeastward subduction of the Cocos oceanic plate beneath the North America plate. Thrust- and normal-type earthquakes are a common occurrence along this plate boundary and the Guatemala region, with events occurring both within the subduction zone and in the overriding plate. Over the past 40 years, 27 events of M6.0 or greater have occurred within 300km of the September 2013 event. Events of note in this region include earthquakes on November 2012 Mw7.4 offshore of Guatemala, which killed 39 people; September 1993 M­w­7.2 offshore of Chiapas, Mexico, which killed one person; and December 1983 Mw7.0 offshore of Guatemala. Other early 20th century earthquakes in the Guatemala region include August 1942 Mw7.9, which killed 38 and April 1902 M7.5, which killed more than 5000 people.


Seismotectonics Of The Caribbean Region And Vicinity.
Extensive diversity and complexity of tectonic regimes characterizes the perimeter of the Caribbean plate, involving no fewer than four major plates (North America, South America, Nazca, and Cocos). Inclined zones of deep earthquakes (Wadati-Benioff zones), ocean trenches, and arcs of volcanoes clearly indicate subduction of oceanic lithosphere along the Central American and Atlantic Ocean margins of the Caribbean plate, while crustal seismicity in Guatemala, northern Venezuela, and the Cayman Ridge and Cayman Trench indicate transform fault and pull-apart basin tectonics. 

Along the northern margin of the Caribbean plate, the North America plate moves westwards with respect to the Caribbean plate at a velocity of approximately 20 mm/yr. Motion is accommodated along several major transform faults that extend eastward from Isla de Roatan to Haiti, including the Swan Island Fault and the Oriente Fault. These faults represent the southern and northern boundaries of the Cayman Trench. Further east, from the Dominican Republic to the Island of Barbuda, relative motion between the North America plate and the Caribbean plate becomes increasingly complex and is partially accommodated by nearly arc-parallel subduction of the North America plate beneath the Caribbean plate. This results in the formation of the deep Puerto Rico Trench and a zone of intermediate focus earthquakes (70-300 km depth) within the subducted slab. Although the Puerto Rico subduction zone is thought to be capable of generating a megathrust earthquake, there have been no such events in the past century. The last probable interplate (thrust fault) event here occurred on May 2, 1787 and was widely felt throughout the island with documented destruction across the entire northern coast, including Arecibo and San Juan. Since 1900, the two largest earthquakes to occur in this region were the August 4, 1946 M8.0 Samana earthquake in northeastern Hispaniola and the July 29, 1943 M7.6 Mona Passage earthquake, both of which were shallow thrust fault earthquakes. A significant portion of the motion between the North America plate and the Caribbean plate in this region is accommodated by a series of left-lateral strike-slip faults that bisect the island of Hispaniola, notably the Septentrional Fault in the north and the Enriquillo-Plantain Garden Fault in the south. Activity adjacent to the Enriquillo-Plantain Garden Fault system is best documented by the devastating January 12, 2010 M7.0 Haiti strike-slip earthquake, its associated aftershocks and a comparable earthquake in 1770. 

Moving east and south, the plate boundary curves around Puerto Rico and the northern Lesser Antilles where the plate motion vector of the Caribbean plate relative to the North and South America plates is less oblique, resulting in active island-arc tectonics. Here, the North and South America plates subduct towards the west beneath the Caribbean plate along the Lesser Antilles Trench at rates of approximately 20 mm/yr. As a result of this subduction, there exists both intermediate focus earthquakes within the subducted plates and a chain of active volcanoes along the island arc. Although the Lesser Antilles is considered one of the most seismically active regions in the Caribbean, few of these events have been greater than M7.0 over the past century. The island of Guadeloupe was the site of one of the largest megathrust earthquakes to occur in this region on February 8, 1843, with a suggested magnitude greater than 8.0. The largest recent intermediate-depth earthquake to occur along the Lesser Antilles arc was the November 29, 2007 M7.4 Martinique earthquake northwest of Fort-De-France. 



USGS earthquake historic seismicity.

The southern Caribbean plate boundary with the South America plate strikes east-west across Trinidad and western Venezuela at a relative rate of approximately 20 mm/yr. This boundary is characterized by major transform faults, including the Central Range Fault and the Boconó-San Sebastian-El Pilar Faults, and shallow seismicity. Since 1900, the largest earthquakes to occur in this region were the October 29, 1900 M7.7 Caracas earthquake, and the July 29, 1967 M6.5 earthquake near this same region. Further to the west, a broad zone of compressive deformation trends southwestward across western Venezuela and central Columbia. The plate boundary is not well defined across northwestern South America, but deformation transitions from being dominated by Caribbean/South America convergence in the east to Nazca/South America convergence in the west. The transition zone between subduction on the eastern and western margins of the Caribbean plate is characterized by diffuse seismicity involving low- to intermediate-magnitude (Magnitude less than 6.0) earthquakes of shallow to intermediate depth. 

The plate boundary offshore of Colombia is also characterized by convergence, where the Nazca plate subducts beneath South America towards the east at a rate of approximately 65 mm/yr. The January 31, 1906 M8.5 earthquake occurred on the shallowly dipping megathrust interface of this plate boundary segment. Along the western coast of Central America, the Cocos plate subducts towards the east beneath the Caribbean plate at the Middle America Trench. Convergence rates vary between 72-81 mm/yr, decreasing towards the north. This subduction results in relatively high rates of seismicity and a chain of numerous active volcanoes; intermediate-focus earthquakes occur within the subducted Cocos plate to depths of nearly 300 km. Since 1900, there have been many moderately sized intermediate-depth earthquakes in this region, including the September 7, 1915 M7.4 El Salvador and the October 5, 1950 M7.8 Costa Rica events. 

The boundary between the Cocos and Nazca plates is characterized by a series of north-south trending transform faults and east-west trending spreading centers. The largest and most seismically active of these transform boundaries is the Panama Fracture Zone. The Panama Fracture Zone terminates in the south at the Galapagos rift zone and in the north at the Middle America trench, where it forms part of the Cocos-Nazca-Caribbean triple junction. Earthquakes along the Panama Fracture Zone are generally shallow, low- to intermediate in magnitude (Magnitude less than 7.2) and are characteristically right-lateral strike-slip faulting earthquakes. Since 1900, the largest earthquake to occur along the Panama Fracture Zone was the July 26, 1962 M7.2 earthquake. -USGS.

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