Mexico City Shook To Its Foundation 25 Years Ago; It will Probably Happen Again September 19, 2010

CLICK ON IMAGE FOR USGS PHOTO LIBRARY OF MEXICO CITY 1985

Original City Was Literally on Lake Texcoco

On This Date in History:  Mexico City has an interesting history.  It is built on the ancient Aztec City of  Tenochtitilan which was built as a water based society really on top of Lake Texcoco through the use of chinampas or water gardens.  When the Spanish showed up in the early 16th century, they eventually conquored the Aztecs and decided that this big lake just would not do.  Lake Texcoco was an enclosed lake and tended to flood the city and beside that it impaired their use of horses.  So, they began projects to drain the lake.  Well, in 1519 the city had 250, 000 inhabitants which was a lot of folks when one considers that London had about 200,000 people and Madrid about 64,000 around the same time.  By the turn of the 20th century, Mexico City still had about the same population that it had in 1519 but by 1953, the city’s population had mushroomed to over 3 million and the area went from 29 square miles to about 150.  Much of the expanded city was on the dry lake bed of Lake Texcoco.   By 1996, Mexico City covered 870 square miles and was home for about 17 million people. 

15 Story Steel Reinforced Nuevo Leon Building Collapsed

Now, with the lake gone and the population rising, water became scarce so they started drilling wells on the old lake bed for water.  The result of the extraction of groundwater has been some serious subsidence.  Beyond that, an old lake bed is not a very stable geological formation on which to build a city.  It has the ability to jiggle alot when shaken.  That makes Mexico City one of the most vulnerable cities in the world when it comes to earthquakes.  On this date in 1985 an earthquake registering 8.0 on the richter scale shook Mexico City and the surrounding region.  The earthquake struck at about 7:17:47 AM on September 19, 1985 releasing about 5.61 x 1024 ergs (10 to the power of 24) or about 19 kilotons of TNT which was about twice as much energy than the Hiroshima atomic bomb.   It was the greatest earthquake event in Mexico since the Great Jalisco Earthquake of 1932.  The geology of the former lake bed is suspected to have contributed to great resonance effects with dominant two second horizontal ground accelerations that were recorded in the area.  The epicenter of the quake was relatively shallow but was 300 km away from Mexico City which is pretty far away in relation to the damage.   Evidence supporting the assertion that the physical characteristics of the earth around Mexico City contributed to the extreme effects is the fact that a large percent of the building damaged or destroyed were between 8 and 18 stories high.  Think of it has buiding a house on jello.   

Steel Reinforced Concrete Suarez Apartments Couldn't Stand

The earthquake was felt as far north as Houston, Texas and as far northwest as El Paso, Texas and all the way in Tuscon, AZ a swimming pool at the University of Arizona lost water due to the sloshing from the vibration.  To the west, a tsunami was generated that was about 3 meters high at Zihuatenejo and 1.4 meters at Acapulco.  That tsunami resonated across the Pacific to Hawaii and even a 5 cm rise was recorded at Tahiti.  An aftershock of magnitude 7.5 on Sept 21 caused a second tsunami, though some geologists suspect that this was a separate earthquake rather than an aftershock.  That is something for academics to argue about because it really makes little difference.  The damage was horrific.  Obviously, severe damage was experienced in Mexico City and the death toll has been pegged in excess of 9500 with some estimates of fatalities approaching 35, 000.  At the time, Mexico City probably had about 15 million people so, when you think about it, the percentage of fatalities vs the total population was pretty small…but when you are talking about such huge numbers. small percentages can translate into large numbers of people.   Like the fatality totals, total casualties may never be known for certain but injuries numbered at least 30,000 and some 100,000 people were left homeless.  412 buildings collapsed and 3124 were severely damaged in Mexico City.  The earthquake affected about 825,000 square miles.  Damage was caused across Central Mexico from Lazaro Cardenas on the Pacific Coast to Vera Cruz on the Gulf Coast. 

Ruins of the Hotel Regis

An interesting aspect of this event was that, initially, the political power of the country said it didn’t need  any help.  The Revolutionary Party had been in power for so long that it was considered by many to be an institution.  But, many political analysts suggest that the governmental early rejection of foreign aid led to the downfall of the Revolutionary Party.  A number of rather somber ceremonies were held today to commemorate what happened in Mexico City 25 years ago with civic memorial services as well as Roman Catholic Masses conducted to remember the dead.  At the location of the Hotel Regis, patrol cars and ambulances lined the streets and turned on their sirens to mark the time of the quake.  That was a particularly imfamous building collapse as shortly following the hotel’s demise, a gas leak fed a fire that made it quite difficult to try to rescue anyone who may have survived.

Notice the Uprooted Foundation of this 8 story building that split in two

The really sad thing is that this type of catostrophe will probably happen again.  When the Spanish first conquored the city they considered moving it but chose not to do so.  The center of the city is really pretty close to the center of the old lake bed and that lake bed has a relatively high water content.  Hence, when there is considerable shaking then liquification of the sediment takes place making it unsuitable to support large structures.  The same thing happened in the landfill areas around San Francisco Bay in the 1991 earthquake there.  In California, there is the San Andreas Fault which makes that part of the US susceptable to earthquakes but Mexico is extremely vulnerable as there’s a lot of constant friction between the North American Plate, the Cocos Plate and the Pacific Plate.  It’s one of the more seismically active regions of the world with some 90 temblors of maginitude 4.o of more recorded on average each year.  Not only is the region active and the dry lakebed not overly stable, the lakebed also has a natural harmonic pitch of about 2.5 which means everything on the lakebed shakes at the same frequency and it just happens that 2.5 is a very common frequency of shallow earthquakes.  Mexico City is kinda like New Orleans, or Los Angeles or Pompeii or Seattle or any of a number of large, urban environments that are extremely vulnerable to natural disasters that have come in the past and will come again in the future.  It’s just part of the risk of living on an active planet.

Filibuster As Part of American Expansion, Not Legislative Tactics July 12, 2010

Americans Filibustered Numerous Times in the 19th Century at Central America's Expense

On this Date In History: American William Walker was a doctor, lawyer, newspaperman and hypnotist in the middle of the 19th Century. But he became better known as a filibuster.   That does not mean that he was a member of Congress.  Today, we think of a filibuster as an interesting idiosyncrasy of the United States Senate that can hold up the entire process of debating and passing legislation.  However, in mid 19th century America, the word “filibuster” had an entirely different meaning for most Americans than the political procedure known to most people today.   

Instead, the word ”filibuster”  is derived from the Dutch word Vrijbuiter that means freebooter or soldier of fortune.   He was a little guy as he weighed all of about 120 pounds but he had big ambitions.  Initially, the object of his quest was Baja California and Sonora in Mexico.  He wanted to create an independent nation there with the ultimate objective being annexation of that region to the United States that would be a slave state. When that failed, he turned his sites elsewhere.   On This Date in 1856, at the age of 31 he became the only American born citizen to become President of another country….supposedly. At least that is what my source claims. I would suggest that Sam Houston as President of the Republic of Texas was first. Anyway, this guy convinced the head of the Democrat party in Nicaragua to invite him and some “settlers” to come to Nicaragua. In reality, they were a bunch of mercenaries hired to help that party win a civil war that was going on. The ruse of being settlers was set up to avoid entanglement in US neutrality laws. So, he and his band of merry men helped defeat the opposition and he set up a phony election that made him president. He only served two years because he irked the wrong guy.

Walker leading the way at Lake Nicaragua

One of the things he was doing was trying to conquer neighboring countries by hiring more mercenaries and also get support from the slave holding South in the United States by rescinding Nicaragua’s long standing Emancipation order. Well, none of that sat well with Americans in the North and particularly Commodore Cornelius Vanderbilt who had a company that ferried freight and passengers across that part of Central America before the canal was built. He even had designs of building a canal across Nicaragua and Walker was in the way. So, he got together a bunch of guys in neighboring Costa Rica and even got help from the British and American Navies. That was the end of Walker who lost a key battle on April 11, 1857 and surrendered on May 1st of that year. He was sent back to the United States where he wrote a book about his adventures. He tried to return and when he did, he was captured again in Honduras by the British Navy who turned him over to local Hondurans who promptly had Walker executed by firing squad at the age of 36 on September 12, 1860.

Walker's Effort Created A Costa Rican National Hero

While we don’t think about William Walker much, his defeat and failure marked a turn around in Central America as it was seen as a pseudo war of independence. His name is one hated as it is held up as a symbol of “Yankee imperialism.” In Costa Rica, there is a national holiday commemorating Walker’s defeat on April 11.   However, Walker’s defeat is not the focus but instead the holiday is set aside to commemorate the exploits of Juan Santamaria, who is said to have done heroic things while barefoot in the battle against Walker.  So, for all his trouble…he got a day in Costa Rica for his failure and they named it for a 19 year-old barefooted soldier: Juan Santamaria Day.   Costa Rica also sports the Juan Santamaria International Airport.  Seems that Walker’s biggest contribution for the Central American country was to place Juan Santamaria in the annals of Costa Rican history.  Take a lesson from this. Don’t try to take over a country. Leave that to the professionals.

Weather Bottom Line:  Rain chances will be elevated for Monday and Tuesday as a shortwave comes out of the Southern Plains.  But, you will note that the chance of rain listed in most forecasts are less than originally posted.  Last night I saw a local broadcast claim a 70% chance of rain today.  I then looked at the data and found that it indicated that the shortwave was not following the track that would give rise to such chances, which means someone didn’t do their homework.  It’s not that there is no chance, but just not as aggressive as had been advertised.  It’s all because of a cold front that is approaching slowly.  So, scattered activity will be in the area for Monday and Tuesday.  The front doesn’t get very far south of us before it slides back north as a warm front and our temperatures and humidity jump for a day or so before another cold front comes down at the end of the week and rain chances go up again.