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Fig. 1.0 "Stunned residents in Aceh Province lay on the streets fearing for more violent shakings and panick-stricken others evacuate to higher grounds in anticipation of a Tsunami.  Image Courtesy: Reuters."

Update: Large Aftershocks Continue To Rattle Northern Sumatra, 7.0 Mb Earthquake Hits Mexico Anew

By: Weatherguy Adonis

Adonis S. Manzan

Tsunami Watch Across Indian Ocean, Atlantic Basin Lifted

Iloilo City, Philippines, 12 April 2012, (0400Z)–Tsunami scare now has past across vast regions in Indian Ocean Basin and farther to Atlantic Ocean.  The Pacific Tsunami Warning Center (PTWC), in Pearl Harbour, Hawaii has issued in its bulletin at around 1236Z (0836PM-PHL), 11 April 2012, that the danger has past, therefore the lifting of such warning was found necessary to ease the concerns along the immediate coasts.  Later, a supplementary bulletin was issued around 1318Z (0918PM-PHL).

These are some of the gallery of photos I got from Reuters Newswires:

Fig. 1.0 "Stunned residents in Aceh Province lay on the streets fearing for more violent shakings and panick-stricken others evacuate to higher grounds in anticipation of a Tsunami. Image Courtesy: Reuters."

Fig. 2.0 A Police officer with a woman trying to evacuate as Tsunami could be racing towards the coast of Aceh Province in Indonesia. Image Courtesy: Reuters."

Fig. 3.0 "In the City of Medan, almost 560 kms North-northeast from the epicenter of the massive 8.6 Mb and 8.2 Mb twin temblors, residents try to calm a woman in distraught as violent tremors have hit the region. Image Courtesy: Reuters."

Fig. 4.0 "Traffic jams the streets in Banda Aceh, the closest region to be hit by the massive twin temblors on 11 April 2012. Image Courtesy: Reuters."

Fig. 5.0 "A local disaster management officer makes contact with grassroots level warning of an impending Tsunami surge along the coastal communities in Colombo, capital of Sri Lanka on Wednesday. Image Courtesy: Reuters."

Fig. 6.0 "Fisherfolks clear the coast as officials in Colombo, Sri Lanka announced the danger of an incoming Tsunami as a result of yesterday's massive twin temblors off Sumatra. Image Courtesy: Reuters."

Fig. 7.0 "Evacuating the poor, bed-ridden patients in a local hospital in Southern Indian City of Chennai. Image Courtesy: Reuters."

The highest “Tsunami waves” on record has struck Suak Uleue, Indonesia at 6.0 m (20 ft) at about 01.26 hrs after the seismic event has commenced off the Northern Sumatran coast along the Sunda Trench.

A maximum read of  Tsunami,” wave height of 1.8 m (6 ft) was recorded in Naibos, Indonesiaat around 01.08 hrs after the initial 8.7 Mb event.  In Meulaboh, Indonesia, a 1.06 m (3.5 ft) was recorded at coastal tide gauges was also registered.

Fig. 8.0 "At the moment of disaster, 0839Z (0539PM-PHL), 11 April 2012. I don't reconcile how the number eleven (11) always have a connection with such extreme of events. Image Courtesy: USGS."

The massive main shock registered a whopping 8.6 Mb, located at about 434 km (270 mi) Southwest of Banda Aceh, the capital of Indonesia’s Aceh province, the U.S. Geological Survey has issued in its website.  The epicenter was pegged to be at a depth of 23 km (14 mi) beneath the surface, making this geologic event one of the most shocking to have hit the region since the historic 26 December 2004’s massive 9.1 Mb Temblor, dubbed “Great Sumatran Earthquake.”

Fig. 9.0 "A graphical representation of where the twin temblors have struck just off the Northern Sumatran coast in Indonesia, sending thousands seeking higher ground in fear of approaching Tsunami. Image Courtesy: UNEC."

Two (2) hours later, a large aftershock has hit of 8.2 Mb, just West coast of Northern Sumatra, which among the closest city centers of Singapore, Bangkok were shaken by the massive tremor, and reports of violent shaking was also observed in several areas across Thailand and Malaysia.  Witnesses lamented the frightening situation as the violence lasted for more than three (3) to five (5) minutes, in an interview with local television network in Bangkok, wherein the high-rise buildings were swaying longer than they have  experienced since the 2004 seismic event.

Fig. 10.0 "Tsunami Travel Times as indicated in a graph by the West Coast of Alaska Tsunami Warning Center (WCATWC), in preparation of the ensuing Tsunami that was later on cancelled. Image Courtesy: WCATWC."

2004 Boxing Day Tsunami Reminisced, Warnings In Place

The 2004 “Boxing Day Tsunami,” was generated across underneath the Indian Ocean, that has left 273,000 dead and thousands injured, and has destroyed the coastal cities and townships along the immediate fourteen (14) countries, costing $10 Billions worth of damages in infrastructure and livelihood, which took place 250 km (155 mi) South-southeast of Banda Aceh at a depth of 30 km (19 mi) beneath the surface.

The said  “Tsunami,” was a singularly most horrendous natural disaster to have struck the region according to the United Nations (UN), which sparked an international relief effort.

Tsunami Warning System was then taken into account and a study was conducted for implementation.  It was carried out to ready the Indian Ocean for yet another seismic event such as this, and evidently has created a huge interest on the aspect of drills conducted and appropriate dissemination to advance the required evacuations when the need arises.

Tsunami Science

“Tsunamis,” are characterized as shallow-water waves.  Shallow-water waves are different from wind-generated waves, the waves many of us have observed on a the beach.  Wind-generated waves usually have period (time between two sucessional waves) of five (5) to twenty (20) seconds and a wavelength (distance between two sucessional waves) of about 100 to 200 m (300 to 600 ft).

Fig. 11.0 "Tsunami waves crest before reaching for the coast. Image Courtesy: ITOC"

A “Tsunami,” can have a period in the range of ten (10) minutes to two (2) hours and a wavelength in excess of  500 km (300 mi).  It is because of their long wavelengths that tsunamis behave as shallow-water waves.  A wave is characterized as a shallow-water wave when the ratio between the water depth and its wavelength gets very small.

The speed of a shallow-water wave is equal to the square root of the product of the acceleration of gravity (32ft/sec/sec or 980cm/sec/sec) and the depth of the water.  The rate at which a wave loses its energy is inversely related to its wavelength.

Since a “Tsunami,” has a very large wave length, it will lose little energy as it propagates.  Hence in very deep water, a “Tsunami” will travel at high speeds and travel great transoceanic distances with limited energy loss.

For example, when the Ocean is 6100 m (20,000 ft) deep, unnoticed “Tsunami,” travel about 890 km/hr (550 mi/hr), at about the speed of a jet airplane.  And they can move from one side of the Pacific Ocean to the other side in less than one day.

As a “Tsunami” leaves the deep water of the open sea and propagates into the more shallow waters near the coast, it undergoes a transformation.  Since the speed of the tsunami is related to the water depth, as the depth of the water decreases, the speed of the tsunami diminishes.  The change of total energy of the tsunami remains constant.  Therefore, the speed of the “Tsunami,” decreases as it enters shallower water, and the height of the wave grows.  Because of this “Shoaling” effect, a “Tsunami” that was imperceptible in deep water may grow to be several feet or more in height.

Huge Earthquake Strikes Off Mexico

Update on yet another massive 7.0 Mb Earthquake that has struck 18.50N-102.65W, at about 52 km South of  Guadalajara in Mexico, with population of 1,640,589, at around 2255.18Z (1755.18PM-local time), or 24 km West of  Arteaga, with population density of 9,550 more or less.  There were no reports of damage or casualties at the moment.

Fig. 12.0 "Huge 7.0 Mb Earthquake struck Western Mexico just hours after the immensely destructive 8.6 Mb and 8.2 Mb Temblors hit just West of Northern Sumatra, Indonesia on 11 April 2012. Image Courtesy: PTWC."

The PTWC has issued an information statement about this seismic event, but no Pacific-wide “Tsunami,” was ever issued to that effect.

This has been your Weatherguy hailing from the Philippines, Mabuhay!  Stay safe guys!

 (Note: If you have queries, email me at amanzan@smartbro.net or through weatherguyadonis@theboplive.net)
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