ประกาศข่าวแผ่นดินไหว(&การคาดการณ์)

แผ่นดินไหวที่นอกฝั่ง Oregon หนึ่งในแผ่นดินไหวที่ใหญ่สุดที่ถูกบันทึกไว้ (US)


US: Oregon's Offshore Earthquake of February 2012: One of the Largest Recorded in the State

Jennifer Young
Decoded Science
Wed, 15 Feb 2012 09:56 CST



© USGS

The Earth moved for many over this Valentine's Day, but not due to romance - a magnitude 6.0 earthquake struck around 250 km off the west coast of Oregon on February 14, 2012. The Valentine's Day quake is notable not only for its size (it is one of the largest ever to have occurred in the state or off its coast) but also in terms of the complex tectonic setting in which it occurred.

The Oregon Earthquake of February 2012

The Oregon earthquake occurred on an ocean ridge, at a divergent boundary - where new crust is created by upward movement of hot and buoyant rock from the earth's interior - between two of the large slabs of crust (tectonic plates) which make up the surface of the earth. Preliminary information from the United States Geological Survey (USGS) shows that the quake occurred at a depth of 10km on the fracture zone associated with the Juan de Fuca Ridge, which marks the western boundary of the Juan de Fuca microplate.

The Tectonic Setting: Divergent Boundaries

Although plate tectonics is generally described in simplistic terms (large crustal plates and single faults) the local situation is inevitably more complex. At its simplest we might describe a setting in which a divergent boundary in the east drives the Juan de Fuca plate westwards against the North American plate, forcing it beneath the North American continent.

In the case of the Juan de Fuca microplate, at least two other small plates, the Explorer Plate to the north and the Gorda plate to the south, are involved. The relative direction, type of movement (with convergent, divergent and conservative boundaries present within a relatively small area) and speed of these plates generates tensions and, ultimately, earthquakes.

© USGS

Earthquake History of Oregon

At M6.0 the February 2012 earthquake is not globally significant but is nevertheless large for an earthquake at an ocean ridge system. In such settings frequent and shallow earthquakes are usually small in magnitude. Although large earthquakes do occur in such zones (the largest recorded being M8.2), major tremors are much more typical of subduction zones.

Interestingly, the recent earthquake also rates as one of the largest recorded in or off Oregon - despite the presence of a subduction zone (the Cascadia subduction zone) immediately off the coast, at the eastern edge of the Juan de Fuca microplate where it bends beneath the North American continent.

Although the whole of the continental west coast was affected by a major earthquake in 1700, Oregon has not in recent years been prone to major earthquakes: the USGS list of major tremors shows only three of M6.0 or more since 1900. Of these the second largest, at M6.3, occurred on the same fracture zone as the event of 2012.

The reason for this is the relatively slow convergence (and in places no convergence at all) of the Juan de Fuca system and North American Plate. Thus, although not significant by global standards, the Oregon 2012 quake will count as a major earthquake in its local context and within its tectonic framework.

Sources

USGS Earthquake Hazards Program. Magnitude 6.0 Off the Coast of Oregon. Magnitude 8 and Greater Earthquakes Since 1900. Accessed February 15, 2012.

 

<table border="0" cellpadding="1" cellspacing="1"><tbody><tr><th align="center">MAG </th> <th align="center">UTC DATE-TIME
y/m/d h:m:s </th> <th align="center">LAT
deg </th> <th align="center">LON
deg </th> <th align="center">DEPTH
km </th> <th> Region</th> </tr> <tr><td nowrap="nowrap" valign="top" align="center">MAP</td><td nowrap="nowrap" valign="top" align="center"> 5.1 </td><td nowrap="nowrap" valign="top" align="center">2012/02/16 02:20:28 </td><td nowrap="nowrap" valign="top" align="right"> -17.851 </td><td nowrap="nowrap" valign="top" align="right"> 65.596 </td><td nowrap="nowrap" valign="top" align="right"> 10.1 </td><td valign="top"> MAURITIUS - REUNION REGION</td></tr></tbody></table>10-degree Map Centered at 20°S,65°E

 

<table class="tbis" border="0" cellpadding="5" cellspacing="0" width="840" align="center"><tbody><tr class="tbis1" bgcolor="#336699"><td nowrap="nowrap" width="130">วัน-เวลา *ประเทศไทย</td> <td nowrap="nowrap" width="40" align="center">ขนาด</td> <td nowrap="nowrap" width="50" align="center">Latitude</td> <td nowrap="nowrap" width="50" align="center">Longitude</td> <td nowrap="nowrap" width="50" align="center">Phase</td> <td nowrap="nowrap" width="">บริเวณที่เกิด</td> <td width="20">
</td> </tr> <tr class="tbis3"> <td valign="top">2555-02-16 12:43:57</td> <td valign="top" align="center">2.4</td> <td valign="top" align="center">19.66</td> <td valign="top" align="center">99.80</td> <td valign="top" align="center">16</td> <td valign="top">อ.พาน จ.เชียงราย</td></tr></tbody></table>

 

ช่วยทำให้ดูง่ายๆ ขึ้น

[ame="http://www.youtube.com/watch?v=2a--NC4Nong"]2/10/2012 -- MUST SEE ! 2011 earthquakes WORLDWIDE plotted and animated (with sound intensity) ! - YouTube[/ame]

 

<table class="tbis" border="0" cellpadding="5" cellspacing="0" width="840" align="center"><tbody><tr class="tbis1" bgcolor="#336699"><td nowrap="nowrap" width="130">วัน-เวลา *ประเทศไทย</td> <td nowrap="nowrap" width="40" align="center">ขนาด</td> <td nowrap="nowrap" width="50" align="center">Latitude</td> <td nowrap="nowrap" width="50" align="center">Longitude</td> <td nowrap="nowrap" width="50" align="center">Phase</td> <td nowrap="nowrap" width="">บริเวณที่เกิด</td> <td width="20">
</td> </tr> <tr class="tbis3"> <td valign="top">2555-02-17 04:57:23</td> <td valign="top" align="center">2.6</td> <td valign="top" align="center">20.67</td> <td valign="top" align="center">97.56</td> <td valign="top" align="center">11</td> <td valign="top">ประเทศพม่า</td></tr></tbody></table>

 

<table class="tbis" border="0" cellpadding="5" cellspacing="0" width="840" align="center"><tbody><tr class="tbis1" bgcolor="#336699"><td nowrap="nowrap" width="130">วัน-เวลา *ประเทศไทย</td> <td nowrap="nowrap" width="40" align="center">ขนาด</td> <td nowrap="nowrap" width="50" align="center">Latitude</td> <td nowrap="nowrap" width="50" align="center">Longitude</td> <td nowrap="nowrap" width="50" align="center">Phase</td> <td nowrap="nowrap" width="">บริเวณที่เกิด</td> <td width="20">
</td> </tr> <tr class="tbis3"> <td valign="top">2555-02-17 11:42:27</td> <td valign="top" align="center">3.1</td> <td valign="top" align="center">20.74</td> <td valign="top" align="center">98.15</td> <td valign="top" align="center">11</td> <td valign="top">ประเทศพม่า</td> <td>
</td> </tr> <tr class="tbis2"> <td valign="top">2555-02-17 04:57:23</td> <td valign="top" align="center">2.6</td> <td valign="top" align="center">20.67</td> <td valign="top" align="center">97.56</td> <td valign="top" align="center">11</td> <td valign="top">ประเทศพม่า</td></tr></tbody></table>