  | |
| UTC time | Doublet earthquake: |
|---|---|
| A: 2006-12-26 12:26:21 | |
| B: 2006-12-26 12:34:15 | |
| ISC event | |
| A:11123554 | |
| B:11123555 | |
| USGS-ANSS | |
| A:ComCat | |
| B:ComCat | |
| Local date | December 26, 2006 (2006-12-26) |
| Local time | |
| A: 20:26 | |
| B: 20:34 | |
| Magnitude | |
| A: 7.0Mw[1] | |
| B: 6.9 Mw | |
| Depth | 10 km (6.2 mi)[1] |
| Epicenter | 21°49′N120°37′E / 21.82°N 120.61°E /21.82; 120.61[1] |
| Areas affected | Taiwan |
| Max. intensity | MMI VIII (Severe)[2] |
| Tsunami | Yes |
| Aftershocks | 5.5mb Dec 26 at 12:40[3] 5.6 Mw Dec 27 at 2:30[3] |
| Casualties | 2 dead; 42 injured |
The2006 Hengchun earthquakes occurred on December 26 at 20:26 and 20:34local time off the southwest coast of Taiwan in theLuzon Strait, which connects theSouth China Sea with thePhilippine Sea. TheInternational Seismological Centre measured the shocks at 7.0 and 6.9 on themoment magnitude scale. The earthquakes not only caused casualties and building damage, but severalsubmarine communications cables were cut, disrupting telecommunication services in various parts of Asia.
Taiwan lies in a zone of complex interaction between thePhilippine Sea plate (PSP) and theEurasian plate (EP). To the north, the PSP issubducting beneath the EP along the line of theRyukyu Trench, forming theRyukyu Volcanic Arc. To the south, in contrast, the EP is subducting beneath the PSP along the line of theManila Trench, forming theLuzon Volcanic Arc. At its northern end the Luzon Arc is colliding with the continental margin of the Eurasian plate as the thicker and more buoyant crust enters the subduction zone. This zone of collision is propagating southwards and theHengchun Peninsula marks the early stages of this process.[4]
The sequence began with the first major earthquake at 12:26:21 (UTC), followed slightly less than eight minutes later by the second main shock at 12:34:15.[5][6] The first event had afocal mechanism indicating rupture along anormal fault, probably within the descending oceanic crust of the Eurasian plate as it bends within the subduction zone. Relocated aftershocks are consistent with a moderately west-dipping normal fault, with an estimated rupture area of 50 km x 35 km. The second event has astrike-slip focal mechanism, probably on a steep NNW–SSE trending, WSW-dipping fault, with an estimated rupture area of 65 km x 30 km. The two rupture areas show little overlap and the second event is likely to have been triggered bystress transfer from the first event. The largest aftershock had a similar mechanism to the second main shock.
News agencies aired reports in southern Taiwan of collapsed houses, building fires, hotel guests being trapped in elevators, and telephone outages due to severed lines. Two people were reported killed and 42 injured. The earthquake was felt all over Taiwan, including the capitalTaipei, 450 km (280 mi) north ofHengchun.[7][8]
Power was knocked out to a reported 3,000 homes, but service was restored within a few hours. As of the following morning, cleanup was already underway.[9]
Fifteen historical buildings, including a Grade 2 elephant site, were damaged in the historic center of Hengchun.[10]
The nearbyMaanshan Nuclear Power Plant was affected by the earthquake. Because of the vigorous vibration, the alarm atReactor #2 was activated, forcing the operators to carry outSCRAM immediately. However, Reactor #1 was not affected and remained operational. After the emergency shutdown of Reactor #2, engineers checked the plant facilities and no problems were found.[11]
Residents in differentdistricts of Hong Kong felt the earthquake. Fearing the collapse of their buildings, people inSham Shui Po,Wong Tai Sin andYuen Long ran into the streets.[12] TheHong Kong Observatory estimated the tremor as having aMercalli intensity of III (Weak) to IV (Light).[13] InMacau, residents called the Office for Meteorological and Geophysical Services to ask whether an earthquake had occurred in their city.[citation needed]
There were no reports of major damage in China, although the quake was felt there. InXiamen, people evacuated their homes and offices to open spaces.[14] The earthquake was also felt in various cities inGuangdong andFujian provinces, including inGuangzhou,Shenzhen,Shantou, andFuzhou.[15]
While this earthquake marked the first time atsunami was detected in Taiwan, the change inwater level was only 25 cm (9.8 in) and no damage was caused.[16] Early reports issued by theJapan Meteorological Agency indicated that the earthquake triggered a 1-metertsunami, which was detected heading for the east coast of the Philippines, withBasco in its likely path.[17] TheHong Kong Observatory also issued tsunami information bulletin,[18] while indicating Hong Kong would likely be unaffected.
The earthquake catastrophically disrupted Internet services in Asia, affecting many Asian countries. Financial transactions, particularly in theforeign exchange market were seriously affected as well.[19][20] The aforementioned disruption was caused by damage to severalsubmarine communications cables.[21]
Chunghwa Telecom stated that an undersea cable off the southern coast had been damaged,[22] interrupting communications (includingIDD, telephone services and internet services) of Taiwan with China, Hong Kong, Malaysia, Singapore, Thailand, and the United States. The international calling capacity was reduced to 40%.[23]
China Telecom reported that several international submarine communications cables had been broken,[24][25] including:
IDD, telephone services, and internet services of China with North America were seriously affected by the earthquake. However,China Telecom announced on December 31 thatIDD services had resumed to normal levels. Internet services had resumed to 70% of normal levels. As the undersea cables to North America were seriously damaged by the earthquake, the quality of internet services depended on the progress ofrepair work.[28]
Starting from dawn on 27 December, connections between foreign websites/servers and Hong Kong internet users kept failing. Wikipedia, search engines, online messengers likeICQ andMSN Messenger, and portals likeGoogle,Yahoo andMSN were largely unavailable. Access toChinese Wikipedia was also cut by the earthquake, as the servers are located in South Korea.[29] Websites located in mainland China, such as xinhuanet.com, the website ofXinhua News Agency, were also inaccessible.
On 29 December, theOffice of the Telecommunications Authority (OFTA) of theHong Kong Government announced thatIDD androaming calls to Taiwan had resumed to 50% of the normal level.IDD androaming calls to otherAsian countries (e.g. South Korea) were slower than normal. Calls from Hong Kong to overseas usingcalling cards experienced the same situation as theIDD androaming calls.[30] However, calling from overseas to Hong Kong usingcalling cards still faced serious congestion.[31]
For internet services, as of December 29, connections to websites in the U.S., South Korea, Japan, and Taiwan were still very slow. However, the situation was improving; sites which could not be accessed before (e.g. Wikipedia,Google, YouTube) were available at extremely slow speeds.[32] Among theinternet service providers in Hong Kong,PCCW'sNetvigator was the slowest to resume enough bandwidth for their users.[33] Therefore, as a temporary remedy, many internet users in Hong Kong usedproxy servers in Australia, Thailand, Spain, and even theUAE and Kuwait to access foreign websites.
As of 31 December, the situation of internet connection had improved. Although sites that were previously unavailable became accessible, connection speeds were still slower than normal.[34]
The earthquake cutPLDT's phone service capacity and connectivity by around 40 percent. The two largest Philippine mobile communications companies (Smart Communications andGlobe Telecom) also reported some international connectivity problems. Some carriers were able to re-route their service.Call centers and otheroutsourced business processes that have become a major industry in the Philippines feared that thecable damage might hamper their operations dramatically; only two centers were totally shut down due to the problems.[35]
In the United States, several networks and bloggers experienced a noticeable reduction in the volume ofspam received after the earthquake. A blogger noted that "one large network in North America saw their mail from Korea drop by 90% and from China by 99%."[36]
Korea Telecom,[26] Malaysia'sTelekom Malaysia[37] andJaring,[38] as well as theCommunications Authority of Thailand,[39] Singapore'sStarHub andSingTel[40] and Brunei's Telbru also reported disruption to most Internet services. In Singapore,search engines and portals likeGoogle,Yahoo,MSN and most websites were virtually unreachable. In Indonesia, Google was not accessible, but Yahoo! and Wikipedia could still be used, though the network connection speed was very slow. Sri Lankan internet services were likewise affected. In Malaysia, there were problems with popular Internet services[41] such asGmail andYahoo News; however, the situation was reported to be improving on 29 December.
According to the Office of the Telecommunications Authority (OFTA) ofHong Kong Government, among the five cable ships deployed, two arrived at the scene. However, one of the two ships experienced a major fault on December 30 afternoon and was under urgent repair inKaohsiung, Taiwan. The repair for the ship was estimated to take about a week. Therefore, the repair for the cables had to be postponed. It was estimated that the first part of the repair of one of the submarine cables would be completed around 16 January 2007. For the other damaged cables, survey and assessment were being arranged and repair of most of the cables is expected to be completed progressively by the end of January 2007.[42][43]IDD services and disrupted internet service in Southeast Asia were mostly restored pending the repairs and rerouted traffic.[44]
Before the completion of the cable repair works, however, some countries had already found alternative methods to restore internet access. For example, by 3 January 2007, Singapore'sSingTel had already fully restored the Internet access provided by them.[45] SingNet, SingTel's subsidiary, which handlesISP services, released an announcement on its homepage, mentioning that "internet access to services such as gaming and video downloading may experience some delays".[46] Whether or not this is related to the earthquake is unknown, albeit likely.
According toChina Daily on 16 January, the repair work might be completed by the end of January, yet heavy winds in theBashi Channel stirred up 10-to-12-meter waves, which made it impossible to resume work.[47]
