diariobombeiro

Tectonic Summary

Seismotectonics of the Philippine Sea and Vicinity

The Philippine Sea plate is bordered by the larger Pacific and Eurasia plates and the smaller Sunda plate. The Philippine Sea plate is unusual in that its borders are nearly all zones of plate convergence. The Pacific plate is subducted into the mantle, south of Japan, beneath the Izu-Bonin and Mariana island arcs, which extend more than 3,000 km along the eastern margin of the Philippine Sea plate. This subduction zone is characterized by rapid plate convergence and high-level seismicity extending to depths of over 600 km. In spite of this extensive zone of plate convergence, the plate interface has been associated with few great (M>8.0) ‘megathrust’ earthquakes. This low seismic energy release is thought to result from weak coupling along the plate interface (Scholz and Campos, 1995). These convergent plate margins are also associated with unusual zones of back-arc extension (along with resulting seismic activity) that decouple the volcanic island arcs from the remainder of the Philippine Sea Plate (Karig et al., 1978; Klaus et al., 1992).

South of the Mariana arc, the Pacific plate is subducted beneath the Yap Islands along the Yap trench. The long zone of Pacific plate subduction at the eastern margin of the Philippine Sea Plate is responsible for the generation of the deep Izu-Bonin, Mariana, and Yap trenches as well as parallel chains of islands and volcanoes, typical of circum-pacific island arcs. Similarly, the northwestern margin of the Philippine Sea plate is subducting beneath the Eurasia plate along a convergent zone, extending from southern Honshu to the northeastern coast of Taiwan, manifested by the Ryukyu Islands and the Nansei-Shoto (Ryukyu) trench. The Ryukyu Subduction Zone is associated with a similar zone of back-arc extension, the Okinawa Trough. At Taiwan, the plate boundary is characterized by a zone of arc-continent collision, whereby the northern end of the Luzon island arc is colliding with the buoyant crust of the Eurasia continental margin offshore China.

Along its western margin, the Philippine Sea plate is associated with a zone of oblique convergence with the Sunda Plate. This highly active convergent plate boundary extends along both sides the Philippine Islands, from Luzon in the north to the Celebes Islands in the south. The tectonic setting of the Philippines is unusual in several respects: it is characterized by opposite-facing subduction systems on its east and west sides; the archipelago is cut by a major transform fault, the Philippine Fault; and the arc complex itself is marked by active volcanism, faulting, and high seismic activity. Subduction of the Philippine Sea Plate occurs at the eastern margin of the archipelago along the Philippine Trench and its northern extension, the East Luzon Trough. The East Luzon Trough is thought to be an unusual example of a subduction zone in the process of formation, as the Philippine Trench system gradually extends northward (Hamburger et al., 1983). On the west side of Luzon, the Sunda Plate subducts eastward along a series of trenches, including the Manila Trench in the north, the smaller less well-developed Negros Trench in the central Philippines, and the Sulu and Cotabato trenches in the south (Cardwell et al., 1980). At its northern and southern terminations, subduction at the Manila Trench is interrupted by arc-continent collision, between the northern Philippine arc and the Eurasian continental margin at Taiwan and between the Sulu-Borneo Block and Luzon at the island of Mindoro. The Philippine fault, which extends over 1,200 km within the Philippine arc, is seismically active. The fault has been associated with major historical earthquakes, including the destructive M7.6 Luzon earthquake of 1990 (Yoshida and Abe, 1992). A number of other active intra-arc fault systems are associated with high seismic activity, including the Cotabato Fault and the Verde Passage–Sibuyan Sea Fault (Galgana et al., 2007).

Relative plate motion vectors near the Philippines (about 80 mm/yr) is oblique to the plate boundary along the two plate margins of central Luzon, where it is partitioned into orthogonal plate convergence along the trenches and nearly pure translational motion along the Philippine Fault (Barrier et al., 1991). Profiles B and C reveal evidence of opposing inclined seismic zones at intermediate depths (roughly 70-300 km) and complex tectonics at the surface along the Philippine Fault.

Several relevant tectonic elements, plate boundaries and active volcanoes, provide a context for the seismicity presented on the main map. The plate boundaries are most accurate along the axis of the trenches and more diffuse or speculative in the South China Sea and Lesser Sunda Islands. The active volcanic arcs (Siebert and Simkin, 2002) follow the Izu, Volcano, Mariana, and Ryukyu island chains and the main Philippine islands parallel to the Manila, Negros, Cotabato, and Philippine trenches.

Seismic activity along the boundaries of the Philippine Sea Plate (Allen et al., 2009) has produced 7 great (M>8.0) earthquakes and 250 large (M>7) events. Among the most destructive events were the 1923 Kanto, the 1948 Fukui and the 1995 Kobe (Japan) earthquakes (99,000, 5,100, and 6,400 casualties, respectively), the 1935 and the 1999 Chi-Chi (Taiwan) earthquakes (3,300 and 2,500 casualties, respectively), and the 1976 M7.6 Moro Gulf and 1990 M7.6 Luzon (Philippines) earthquakes (7,100 and 2,400 casualties, respectively). There have also been a number of tsunami-generating events in the region, including the Moro Gulf earthquake, whose tsunami resulted in more than 5000 deaths.

Parameter	Value	Uncertainty
Magnitude	7.9 Mwp	Not Specified
Location	10.828°N, 126.677°E	± 13.7 km
Depth	34.9 km	± 5.8 km
Number of Stations Used	486
Number of Phases Used	486
Minimum Distance	433.0 km (3.89°)
Travel Time Residual	1.00 sec
Azimuthal Gap	13°
Review Status	REVIEWED
Event ID	usc000cc5m

000
WEHW40 PHEB 311258
TSUHWX
HIZ001>003-005>009-012>014-016>021-023>026-311458-
/O.CAN.PHEB.TS.W.0001.000000T0000Z-000000T0000Z/
/O.NEW.PHEB.TS.A.0001.120831T1257Z-000000T0000Z/

BULLETIN
TSUNAMI MESSAGE NUMBER   1
NWS PACIFIC TSUNAMI WARNING CENTER EWA BEACH HI
257 AM HST FRI AUG 31 2012

TO - CIVIL DEFENSE IN THE STATE OF HAWAII

SUBJECT - TSUNAMI WATCH

A TSUNAMI WATCH IS ISSUED FOR THE STATE OF HAWAII EFFECTIVE AT
0257 AM HST.

AN EARTHQUAKE HAS OCCURRED WITH THESE PRELIMINARY PARAMETERS

   ORIGIN TIME - 0248 AM HST 31 AUG 2012
   COORDINATES - 10.9 NORTH  127.1 EAST
   LOCATION    - PHILIPPINE ISLANDS REGION
   MAGNITUDE   - 7.9  MOMENT

EVALUATION

 BASED ON ALL AVAILABLE DATA A TSUNAMI MAY HAVE BEEN GENERATED BY
 THIS EARTHQUAKE THAT COULD BE DESTRUCTIVE ON COASTAL AREAS EVEN
 FAR FROM THE EPICENTER. AN INVESTIGATION IS UNDERWAY TO DETERMINE
 IF THERE IS A TSUNAMI THREAT TO HAWAII.

 IF TSUNAMI WAVES IMPACT HAWAII THE ESTIMATED EARLIEST ARRIVAL OF
 THE FIRST TSUNAMI WAVE IS

                     1228 PM HST FRI 31 AUG 2012

MESSAGES WILL BE ISSUED HOURLY OR SOONER AS CONDITIONS WARRANT.

$$

000
WEAK53 PAAQ 311257
TIBAK1

PUBLIC TSUNAMI INFORMATION STATEMENT NUMBER 1
NWS WEST COAST/ALASKA TSUNAMI WARNING CENTER PALMER AK
557 AM PDT FRI AUG 31 2012

...THIS TSUNAMI INFORMATION STATEMENT IS FOR ALASKA/ BRITISH
   COLUMBIA/ WASHINGTON/ OREGON AND CALIFORNIA ONLY...

NO WARNING... NO WATCH AND NO ADVISORY IS IN EFFECT FOR
THESE AREAS.

EARTHQUAKES OF THIS SIZE ARE KNOWN TO GENERATE TSUNAMIS
POTENTIALLY DANGEROUS TO COASTS OUTSIDE THE SOURCE REGION.
THE WEST COAST/ALASKA TSUNAMI WARNING CENTER IS INVESTIGATING
THE EVENT TO DETERMINE THE LEVEL OF DANGER. MORE INFORMATION
WILL BE ISSUED AS IT BECOMES AVAILABLE.

AT 548 AM PACIFIC DAYLIGHT TIME ON AUGUST 31 AN EARTHQUAKE WITH
PRELIMINARY MAGNITUDE 7.9 OCCURRED
IN THE PHILIPPINE ISLANDS REGION.

PACIFIC COASTAL REGIONS OUTSIDE CALIFORNIA/ OREGON/ WASHINGTON/
BRITISH COLUMBIA AND ALASKA SHOULD REFER TO THE PACIFIC TSUNAMI
WARNING CENTER MESSAGES FOR INFORMATION ON THIS EVENT AT
PTWC.WEATHER.GOV.

MESSAGES WILL BE ISSUED HOURLY BY THE WCATWC UNTIL THE EVENT
STATUS IS UPGRADED TO A WARNING OR ADVISORY OR UNTIL THE CENTER
HAS DETERMINED THAT THE EVENT POSES NO THREAT TO THE CALIFORNIA/
OREGON/ WASHINGTON/ BRITISH COLUMBIA AND ALASKA COASTS. SEE THE
WEB SITE WCATWC.ARH.NOAA.GOV FOR BASIC TSUNAMI INFORMATION -
SAFETY RULES AND TSUNAMI TRAVEL TIMES.

$$

000
WEPA43 PAAQ 311257
TIBWCA

TSUNAMI INFORMATION STATEMENT NUMBER 1
NWS WEST COAST/ALASKA TSUNAMI WARNING CENTER PALMER AK
557 AM PDT FRI AUG 31 2012

...THIS TSUNAMI INFORMATION STATEMENT IS FOR ALASKA/ BRITISH
   COLUMBIA/ WASHINGTON/ OREGON AND CALIFORNIA ONLY...

NO WARNING... NO WATCH AND NO ADVISORY IS IN EFFECT FOR
THE STATES AND PROVINCES PREVIOUSLY LISTED.

EVALUATION
 EARTHQUAKES OF THIS SIZE ARE KNOWN TO GENERATE TSUNAMIS
 POTENTIALLY DANGEROUS TO COASTS OUTSIDE THE SOURCE REGION.
 THE WEST COAST/ALASKA TSUNAMI WARNING CENTER IS INVESTIGATING
 THE EVENT TO DETERMINE THE LEVEL OF DANGER. MORE INFORMATION
 WILL BE ISSUED AS IT BECOMES AVAILABLE.

PRELIMINARY EARTHQUAKE PARAMETERS
 MAGNITUDE - 7.9
 TIME      - 0448 AKDT AUG 31 2012
             0548  PDT AUG 31 2012
             1248  UTC AUG 31 2012
 LOCATION  - 10.9 NORTH 127.1 EAST
           - PHILIPPINE ISLANDS REGION
 DEPTH     - 21 MILES/33 KM

PACIFIC COASTAL REGIONS OUTSIDE CALIFORNIA/ OREGON/ WASHINGTON/
BRITISH COLUMBIA AND ALASKA SHOULD REFER TO THE PACIFIC TSUNAMI
WARNING CENTER MESSAGES FOR INFORMATION ON THIS EVENT AT
PTWC.WEATHER.GOV.

MESSAGES WILL BE ISSUED HOURLY TO KEEP YOU INFORMED OF
THE PROGRESS OF THIS EVENT. REFER TO THE INTERNET SITE
WCATWC.ARH.NOAA.GOV FOR MORE INFORMATION.

$$

000
WEPA40 PHEB 311255
TSUPAC

TSUNAMI BULLETIN NUMBER 001
PACIFIC TSUNAMI WARNING CENTER/NOAA/NWS
ISSUED AT 1255Z 31 AUG 2012

THIS BULLETIN APPLIES TO AREAS WITHIN AND BORDERING THE PACIFIC
OCEAN AND ADJACENT SEAS...EXCEPT ALASKA...BRITISH COLUMBIA...
WASHINGTON...OREGON AND CALIFORNIA.

... A TSUNAMI WARNING AND WATCH ARE IN EFFECT ...

A TSUNAMI WARNING IS IN EFFECT FOR

 INDONESIA / PHILIPPINES / BELAU / YAP / TAIWAN / JAPAN / GUAM /
 N. MARIANAS / PAPUA NEW GUINEA

A TSUNAMI WATCH IS IN EFFECT FOR

 CHUUK / MARCUS IS. / KOSRAE / POHNPEI / MARSHALL IS. /
 WAKE IS. / SOLOMON IS. / RUSSIA / NAURU

FOR ALL OTHER AREAS COVERED BY THIS BULLETIN... IT IS FOR
INFORMATION ONLY AT THIS TIME.

THIS BULLETIN IS ISSUED AS ADVICE TO GOVERNMENT AGENCIES.  ONLY
NATIONAL AND LOCAL GOVERNMENT AGENCIES HAVE THE AUTHORITY TO MAKE
DECISIONS REGARDING THE OFFICIAL STATE OF ALERT IN THEIR AREA AND
ANY ACTIONS TO BE TAKEN IN RESPONSE.

AN EARTHQUAKE HAS OCCURRED WITH THESE PRELIMINARY PARAMETERS

 ORIGIN TIME -  1248Z 31 AUG 2012
 COORDINATES -  10.9 NORTH  127.1 EAST
 DEPTH       -   33 KM
 LOCATION    -  PHILIPPINE ISLANDS REGION
 MAGNITUDE   -  7.9

EVALUATION

 IT IS NOT KNOWN THAT A TSUNAMI WAS GENERATED. THIS WARNING IS
 BASED ONLY ON THE EARTHQUAKE EVALUATION. AN EARTHQUAKE OF THIS
 SIZE HAS THE POTENTIAL TO GENERATE A DESTRUCTIVE TSUNAMI THAT CAN
 STRIKE COASTLINES NEAR THE EPICENTER WITHIN MINUTES AND MORE
 DISTANT COASTLINES WITHIN HOURS. AUTHORITIES SHOULD TAKE
 APPROPRIATE ACTION IN RESPONSE TO THIS POSSIBILITY. THIS CENTER
 WILL MONITOR SEA LEVEL DATA FROM GAUGES NEAR THE EARTHQUAKE TO
 DETERMINE IF A TSUNAMI WAS GENERATED AND ESTIMATE THE SEVERITY OF
 THE THREAT.

ESTIMATED INITIAL TSUNAMI WAVE ARRIVAL TIMES AT FORECAST POINTS
WITHIN THE WARNING AND WATCH AREAS ARE GIVEN BELOW. ACTUAL
ARRIVAL TIMES MAY DIFFER AND THE INITIAL WAVE MAY NOT BE THE
LARGEST. A TSUNAMI IS A SERIES OF WAVES AND THE TIME BETWEEN
SUCCESSIVE WAVES CAN BE FIVE MINUTES TO ONE HOUR.

 LOCATION         FORECAST POINT     COORDINATES     ARRIVAL TIME
 --------------------------------    ------------    ------------
 INDONESIA        GEME                4.6N 126.8E    1335Z 31 AUG
                  BEREBERE            2.5N 128.7E    1353Z 31 AUG
                  PATANI              0.4N 128.8E    1419Z 31 AUG
                  SORONG              0.8S 131.1E    1438Z 31 AUG
                  MANOKWARI           0.8S 134.2E    1447Z 31 AUG
                  WARSA               0.6S 135.8E    1450Z 31 AUG
                  JAYAPURA            2.4S 140.8E    1538Z 31 AUG
 PHILIPPINES      LEGASPI            13.2N 123.8E    1338Z 31 AUG
                  DAVAO               6.8N 125.7E    1340Z 31 AUG
                  PALANAN            17.1N 122.6E    1353Z 31 AUG
 BELAU            MALAKAL             7.3N 134.5E    1407Z 31 AUG
 YAP              YAP_IS.             9.5N 138.1E    1417Z 31 AUG
 TAIWAN           TAITUNG            22.7N 121.2E    1441Z 31 AUG
                  HUALIEN            24.0N 121.7E    1446Z 31 AUG
                  HUALIEN            24.0N 121.6E    1446Z 31 AUG
                  CHILUNG            25.2N 121.8E    1524Z 31 AUG
 JAPAN            OKINAWA            26.2N 127.8E    1502Z 31 AUG
                  SHIMIZU            32.8N 133.0E    1605Z 31 AUG
                  KATSUURA           35.1N 140.3E    1646Z 31 AUG
                  KUSHIRO            42.9N 144.3E    1746Z 31 AUG
                  HACHINOHE          40.5N 141.5E    1753Z 31 AUG
 GUAM             GUAM               13.4N 144.7E    1517Z 31 AUG
 N. MARIANAS      SAIPAN             15.3N 145.8E    1533Z 31 AUG
 PAPUA NEW GUINE  VANIMO              2.6S 141.3E    1539Z 31 AUG
                  WEWAK               3.5S 143.6E    1611Z 31 AUG
                  MANUS_IS.           2.0S 147.5E    1637Z 31 AUG
                  MADANG              5.2S 145.8E    1656Z 31 AUG
                  KAVIENG             2.5S 150.7E    1700Z 31 AUG
                  RABAUL              4.2S 152.3E    1734Z 31 AUG
                  KIETA               6.1S 155.6E    1753Z 31 AUG
                  AMUN                6.0S 154.7E    1806Z 31 AUG
                  LAE                 6.8S 147.0E    1810Z 31 AUG
 CHUUK            CHUUK_IS.           7.4N 151.8E    1646Z 31 AUG
 MARCUS IS.       MARCUS_IS.         24.3N 154.0E    1649Z 31 AUG
 KOSRAE           KOSRAE_IS.          5.5N 163.0E    1740Z 31 AUG
 POHNPEI          POHNPEI_IS.         7.0N 158.2E    1744Z 31 AUG
 MARSHALL IS.     ENIWETOK           11.4N 162.3E    1756Z 31 AUG
                  KWAJALEIN           8.7N 167.7E    1811Z 31 AUG
                  MAJURO              7.1N 171.4E    1843Z 31 AUG
 WAKE IS.         WAKE_IS.           19.3N 166.6E    1757Z 31 AUG
 SOLOMON IS.      FALAMAE             7.4S 155.6E    1804Z 31 AUG
                  PANGGOE             6.9S 157.2E    1809Z 31 AUG
                  GHATERE             7.8S 159.2E    1837Z 31 AUG
                  MUNDA               8.4S 157.2E    1854Z 31 AUG
 RUSSIA           URUP_IS            46.1N 150.5E    1824Z 31 AUG
 NAURU            NAURU               0.5S 166.9E    1843Z 31 AUG


Fonte: USGS 

BULLETINS WILL BE ISSUED HOURLY OR SOONER IF CONDITIONS WARRANT.
THE TSUNAMI WARNING AND WATCH WILL REMAIN IN EFFECT UNTIL
FURTHER NOTICE.

THE JAPAN METEOROLOGICAL AGENCY MAY ALSO ISSUE TSUNAMI MESSAGES
FOR THIS EVENT TO COUNTRIES IN THE NORTHWEST PACIFIC AND SOUTH
CHINA SEA REGION.  IN CASE OF CONFLICTING INFORMATION... THE
MORE CONSERVATIVE INFORMATION SHOULD BE USED FOR SAFETY.

THE WEST COAST/ALASKA TSUNAMI WARNING CENTER WILL ISSUE PRODUCTS
FOR ALASKA...BRITISH COLUMBIA...WASHINGTON...OREGON...CALIFORNIA.