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Magnitude 5.6 - GUERRERO, MEXICO

2009 April 27 16:46:30 UTC

Versión en Español

Earthquake Details

Magnitude 5.6
Date-Time
Location 17.144°N, 99.363°W
Depth 48.7 km (30.3 miles)
Region GUERRERO, MEXICO
Distances 45 km (30 miles) SSE of Chilpancingo, Guerrero, Mexico
65 km (40 miles) ENE of Acapulco, Guerrero, Mexico
135 km (85 miles) S of Iguala, Guerrero, Mexico
250 km (155 miles) S of MEXICO CITY, D.F., Mexico
 
Location Uncertainty horizontal +/- 4.4 km (2.7 miles); depth +/- 9.9 km (6.2 miles)
Parameters NST=251, Nph=251, Dmin=>999 km, Rmss=0.95 sec, Gp= 90°,
M-type=teleseismic moment magnitude (Mw), Version=7
Source
  • USGS NEIC (WDCS-D)
     
Event ID us2009fya9
  • This event has been reviewed by a seismologist.
  • Did you feel it? Report shaking and damage at your location. You can also view a map displaying accumulated data from your report and others.

 

 

                                                                                                                     Tropical Cyclones

 

(Extract from the book Natural Disaster Management)

This article addresses specific windstorm known as tropical cyclones, their inherent potential for damage and society’s efforts for damage reduction through preparedness, mitigation and education.

Tropical cyclones are large-scale weather systems developing over tropical or subtropical waters, where organized surface wind circulation is present. Depending on central sustained wind speed these may be classified as depression, storms or hurricanes,

Behold the atmosphere

One important function of the atmosphere is in distributing energy, coming from the Sun, and in attempting to balance temperature, pressure and moisture around the planet. The atmosphere moves air to carry heat away from the tropics, a band of earth reaching to 23o27' north and south of the equator, toward the polar regions where it is cooler. It is beyond the scope of this text to describe in detail how this redistribution of heat takes place. However it is important to note that it involves a divergent component resulting in the movement of air away from the tropics, and a rotational wind component resulting from the vorticity generated by the Earth's rotation. This mechanism involves the large-scale motion known as tropical circulation and the interaction of the atmosphere with the oceans and land masses.

One area of concern is the interaction of atmospheric processes with human activity. Although uncertainty remains, there is an accumulation of scientific empirical data suggesting that human activity may be contributing to changes in atmospheric balance. This may affect climate and extreme weather events, if it is not doing so already. In consequence, humankind must be observant of its role in altering important natural processes and the need for corrective and timely actions.

Tropical cyclones are needed

Tropical cyclones are needed as an effective method, or safety valve, for dissipating heat accumulated in the ocean and in the tropical regions of the atmosphere. This need is evidenced by the fact that most hurricanes take place during summer and autumn, when the tropics reach their highest temperatures. It is then that the coupled atmosphere-ocean heat transfer engine must be most effective in diverting heat toward the polar regions. In some countries there is a consequential need for tropical cyclones which result from the rains associated with these systems, that are critical for the irrigation of crops and the production of foodstuffs to feed many millions of people.

Cyclogenesis

Cyclogenesis refers to the formation of cyclones. To the combination of conditions needed for cyclone formation, the area where such conditions may be present, and to triggering events as well.    Although the main conditions and favourable areas for tropical cyclogenesis and triggering events have been identified, the genesis of tropical cyclones is still poorly understood. In general, tropical cyclogenesis requires:

These conditions are generally present in tropical waters during summer and early fall, giving rise to an accelerated transfer of heat from the sea surface to the tropical atmosphere creating the energy source for tropical cyclones. Despite these ubiquitous conditions tropical cyclones do not form spontaneously, outside triggers are needed. In the Atlantic tropical cyclones are most often triggered by atmospheric waves moving westward over sub-Saharan Africa.

Other phenomena, often extra-regional, have significant influence on cyclogenesis. For example, tropical cyclone formation in the North Atlantic is related to periodic El Nino events in the Pacific and related to drought in the Sahel region of Africa. Empirical data clearly shows these connections, but they are not yet fully understood.

Even under ideal conditions tropical cyclones are relatively rare, with an average of 80 such systems forming all over the globe in six areas known as tropical cyclone basins that include:    A large portion of the North Atlantic (including the Caribbean and Gulf of Mexico), The Western North Pacific, The Eastern North Pacific, The Northern Indian Ocean, The Southern Indian Ocean, and The Southwest Pacific/Australia region.

Vulnerability

Vulnerability results from the interaction of human activity with hazards. With few exceptions, most coastal and island regions of the world are vulnerable to tropical cyclones. Vulnerability to tropical cyclones can be absolute or relative. Absolute vulnerability is a function of location. For example: islands in the western Caribbean are vulnerable to hurricanes by virtue of being located in the path of such weather events. Relative vulnerability involves exposure to consequential hazards resulting from the interaction of local factors, such as topographic relief, and components of tropical cyclones such as high winds or storm surge. Such consequential hazards include flash floods, mud-slides and beach erosion. With regards to adverse impacts from tropical cyclone on a given location, vulnerability must be viewed, analysed and understood, from a range of perspectives including: a) physical, b) ecological, c) structural, d) social (human), e) economic, and f) political aspects.