Tectonic Setting Indonesia dan Pemodelan gempa dan Tsunami

Pelatihan Pemodelan Tsunami Run-up, RISTEK, 20 Agustus, 2007

Tectonic Setting Indonesia dan Pemodelan gempa dan Tsunami

Danny Hilman Natawidjaja Geoteknologi LIPI

Indonesia kaya SDA dan bencana • Gempabumi • Tsunami • Letusan gunung api • Longsor • Banjir • Angin topan • Badai • Kebakaran hutan alam, dll.

Danny H. Natawidjaja – RUTI 2005

Mitigating Earthquake and Tsunami HAZARDS

SOURCE • • • •

What? Where ? How big ? When?

Banyak disepelekan!

PHYSICAL MODELING

• • • • •

Surface faulting Shaking Tsunami Landslides liquefaction

Model Tsunami (Run-up) yang baik • Input data sumber gempa/tsunami yang dapat dipertanggung jawabkan • Pemilihan scenario parameter sumber yang masuk akal secara ilmiah • Data bathimetri dan topografi serta tutupan lahan yang se-akurat mungkin • Mengerti keterbatasan pemodelan tsunami, baik karena simplifikasi matematis dari proses alam juga karena asumsi-asumsi yang dipakai yang disebabkan ketidaktahuan data sumber yang sebenarnya

DATA CONSTRAINTS ON TSUNAMI MODEL PARAMETER DASAR: • Bathimetri • topografi (utk run-up modeling) PARAMETER UTAMA SUMBER • geometri sumber: panjang-lebar, lokasi • arah dan besar pergerakan • pengangkatan dan penurunan muka bumi • arah rupture dan cepatnya pergerakan

60 – 50 mm/year

PARAMETER SEKUNDER: • Cabang patahan di dekat palung • longsoran di bawah laut

Eurasian Plate Pacific Plate 12 cm/yr

5-6 cm/yr

India-Australian Plate Indonesia is an earthquake country :

Crustal motions from GPS (Bock et al, 2004)

Earthquake in Indonesia since 1964

trench

Forearc islands

Moho

Megathrust earthquake

ZONA SUBDUKSI

It is like a spring board! Interseismic period (slow strain accumulation)

Slow uplift

Slow Submergence

It is like a spring board! Co-seismic = earthquake (sudden strain release)

Sudden Uplift

Co-seismic = earthquake (sudden strain release) Initial Tsunami Formation

Locking zone (=seismic zone= zone of strain accum.)

Depth<60km

Tsunami modeling Shoreline interaction Bathi & topo detil Wave-propagation: F(depth)

SOURCE Fault parameters

Epicenter data of Aceh earthquake 2004 – 1 day after

Max. slip 20m

M 8.9

Preliminerary Rupture Source Model of Dec 2004 Aceh Earthquake Chen JI - Caltech

The early model of Aceh Tsunami 2004 (Steve Ward)

ANIMATION of The 2004 Aceh tsunami (Hamzah Latief)

Ward ChenJi

Vertical displacement of seafloor estimated by Hirata et al. [2005] from satellite altimetry data.

Tsunami source base on the Altimetry Data

(Tsunami Research Group Marine Research Center ITB)

We have used

METHODS OF STUDYING THE SOURCE records of sea-level change in corals

and satellite imagery GPS

To understand the behavior of the tsunami source

Model G Mw9.2 Rupture: • ~1600km long • 10 – 30 meter Displacement westward Based on: • Coral Satelite imagery analysis • GPS campaign mode • Continuous GPS (far field) (after Chlieh et al, 2005 and Subarya et al, Nature, March 2006)

Source parameters Of Aceh Tsunami 2004

• The greatest uplift occurred west of the Nicobar islands and southwest of Aceh

Courtesy of Mohamed Chlieh

Uplift in 2004

Mengenal sumber gempa-tsunami Indonesia

Gempa Sumatra (yg paling banyak dipelajari)

trench

Forearc islands

Sumatran Fault Zone

Moho

Megathrust earthquake

Sumatran earthquake (the most well understood)

1941 (7.9)

2004 (M9.15) 1881 (7.9)

2002

Sumatran fault Zone

1907 (~M7.8)1861

2005 (M 8.7)

EURASIAN PLATE

Malaysia

(M~8.5)

1935 (M7.7)

1797 (M8.4) 1833 (8.9)

Currently locked, Near end of cycle section Jakarta

2000 (M7.8)

te e n t a l P r a vem e o /y m m 0m 6 – 50

Un known section, INDIAN-AUSTRALIAN No large eartquakes in PLATE Historical records

Briggs et al., Science, 2006

the 2004 earthquake

the 2005 earthquake

Paleoseismic history Simeulue island uplift tsunami

SIMELUE ISLAND

1861

uplift

1799

uplift

1400

uplift

965

Similar to dates of uplifted coral and subsided mangrove in the Andaman islands (Rajendran et al 2007) Similar to dates of uplifted coral terrace in the Andaman islands and possible tsunami deposit on east coast of India (Rajendran et al 2007)

Paleoseismic history Simeulue island SE Simelue: uplift tsunami uplift

1861 1799

NW Simelue:

SIMELUE ISLAND

NW: 400 to 600 year recurrence?

SE: 140 to 200 year recurrence?

uplift

1400

uplift

965

Drawn beach north of Calang, Aceh area, July 2007

Paleotsunami study in Banda Aceh area, July 2007

t Ba f ee l au t

A tear in the over-riding plate?

t Ba

March 28,2005

f ee l au t

Slip on the megathrust

Rupture/sumber gempa

Model sumber gempa di zona subduksi

A

A’ hingeline subsidence

uplift Ru

pt u

re

zo ne

A

A’ hingeline subsidence

uplift Ru

pt u

re

zo ne

May 2005

January 2005 Near Afulu village, west coast of Nias island

The March 2005 event resulted in impressive uplift …

Old high tide

Old low tide

Examples from Nias, Simeulue and the Banyak islands

Old high tide New high tide

… dan wilayah di timurnya turun

Haloban village, Banyak islands

But, how about big tsunami in 1861 Nias earthquake?

A Historical sketch of the 1861 earthquake in Nias

t Ba

March 28,2005

f ee l au t

1861?

Slip on the megathrust

Dimana Selanjutnya?

Segmen Mentawai !!!

Stress Shadow dan Efek pemicuan gempabumi (Mc Closkey)

Coastlines show subsidence of the Mentawais for many decades

In Mentawai Island

Evidence Evidence for for giant giant earthquakes earthquakes in in 1797 1797 and and 1833 1833 Fossil microatolls in the intertidal zone, east coast of North Pagai island

~1600

Elevation relative to modern sea level (cm)

~1370

1797 & 1833

Paleogeodetic For ~700 years The Mentawai patch appears to be timepredictable and near failure

Years (AD)

SEISMIC Before AcehAndaman Earthquake

GAP:

Malaysia

ra at m Su

SEISMIC After Aceh –Andaman Earthquake

GAP:

Malaysia

Before Nias Earthquake

ra at m Su

SEISMIC After Nias Earthquake

GAP:

Is Malaysia

Mentawai Seismic gap

ra at m Su

How about Jawa ??

SuGAr Velocity Field Up to June 2006

Ongoing Post-slip

Ongoing Squeezing Of Mentawai

This locked patch broke in 2005 These locked patches are the likely source of the next great Mentawai earthquake and tsunami

Chlieh et al (in review) J Geophys Res

Padang in 1797 (~4,000 people)

Padang now (~800,000 people)

Photo: Jose Borrero

Earthquake and Tsunami Scenarios for Western part of Sumatra

1797

1833

Scenario 1

Scenario 2

Scenario 3

Scenario 4

Patterns of Uplift of the seafloor produced by the six megathrust ruptures scenarios (Borero et al, 2006)

D.H. Natawidjaja May 2007

Animasi proses deformasi gempa dan tsunami



Tidak Surut dulu

Surut dulu

Surut dulu

Tsunami simulation for an Aceh-2004-like source

Scenario 3: Uplift from 20 m slip on 700-km megathrust rupture (Borero et al, 2006)

20-m Slip Scenario in Padang


10-m Slip Scenario in Padang

20-m Slip Scenario in Bengkulu


10-m scenario

20-m scenario

20-m scenario Turun 0.5 meter

10-m scenario

20-m scenario

20-m scenario Turun 1.5 meter

Sumber Gempa - Tsunami Jawa (sedikit tahu, banyak tidaknya)

SUMARY OF JAVA EARTHQUAKE 1840 – 2005 (modified from Newcomb and McCann, 1987)

1994 (Pancer) M 7.8

Time

2006 tsunami M7.8)

• Very old subducted oceanic crust (~150 million years old) •Less-frequent earthquakes and no M≥8 EQ in the history • But what did not happen does not mean would not happen

It lead to a big question… What is the maximum magnitude of earthquake of the Jawa Subduction zone?

July 2006 (Mw 7.8)

SEISM IC GAP

Is it actually less than M8? How about in a much longer time??

1994 (Mw 7.8)

Seismic record for the past 30 years

Bagaimana memilih tsunami source Yang tepat untuk Selatan Jawa???

M 7.8


M 7.8


M 7.8


M 9.0


M 9.0

Gempa Jakarta 1699


Historical On-land Earthquakes of Jawa (Natawidjaja, 2006)

Gempa Jakarta !!! Hikayat Jakarta / Willard A. Hanna. Yayasan Obor Indonesia. 1988 Ed. 1 ISBN 979-461019-4 Pada akhir abad ke-18, citra Ratu Timur itu menurun drastis. Willard A. Hanna (Hikayat Jakarta) mencatat, bahwa kejadian itu diawali oleh gempa bumi yang bukan main dahsyatnya, malam tanggal 4 dan 5 November 1699, yang menyebabkan kerusakan besar pada gedung-gedung dan mengacaukan persediaan air dan memporak-porandakan sistem pengaliran air di seluruh daerah. Gempa itu disertai letusanletusan gunung api dan hujan abu yang tebal, yang menyebabkan terusan-terusan menjadi penuh lumpur. Aliran sungai Ciliwung berubah dan membawa sekian banyak endapan ke tempat dimana sungai itu mengalir ke laut, sehingga kastil yang semula berbatasan dengan laut, seakan-akan mundur sedikit-dikitnya 1 kilometer ke arah pedalaman. ………

Gempa-Tsunami di Indonesia Timur (sumber-nya paling potensial tapi sangat kurang dipelajari)

Earthquake and Tsunami of East Indonesia Region

Active Tectonics


Active Tectonics



Earthquakes M>5: 1964-2006 (Engdahl, 2006)

< 30 km depth 30 - 60 km



Recent Earthquake Mw > 7 since 1973



Historical Earthquake since 1600 (USGS)



Tsunamigenic earthquake zones and Historical Tsunami


Tsunami database from H.Latief

Historical Tsunami: Year (Run-up in m)


Tsunami database from H.Latief

Historical Tsunami: Year (death)

M

8. 0

Bagaimana dengan tsunami source untuk wilayah Maluku?

M

8. 0



M 8.0


M9

Probability map of tsunami-height hazards in Southeast Asia

Paul Sommervile & Hng Kie Thio (URS)

Hanya memakai Data seismic dari tahun 1973??

Anda percaya ??? Bagaimana kualitas data sumber yang digunakan? Data from URS

Concluding remarks RESEARCH

Knowledge of Earthquake and Tsunami Sources,

HAZARD-RISK MODELS

Designing Observation Network and System for Research and Early Warning System

Public Education and Community Preparedness

Tsunami modeling

Infrastructure changes, Evacuation plan, and Post-Disaster actions

Terima Terima kasih kasih

Tunas kelapa yang tumbuh setelah gempa Maret 2005, P. Wunga, Nias, Juni 2006

Tectonic Setting Indonesia dan Pemodelan gempa dan Tsunami

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