Tectonic Setting Indonesia dan Pemodelan gempa dan Tsunami

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Tectonic Setting Indonesia dan

Pemodelan gempa dan Tsunami

Danny Hilman Natawidjaja Geoteknologi LIPI

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Indonesia kaya SDA dan bencana

• Gempabumi

• Tsunami

• Letusan gunung api

• Longsor

• Banjir

• Angin topan

• Badai

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Mitigating Earthquake and Tsunami

• What?

• Where ?

• How big ?

• When?

• Surface faulting

• Shaking

• Tsunami

• Landslides

• liquefaction

SOURCE

HAZARDS

Banyak disepelekan!

PHYSICAL

MODELING

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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

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60 – 50 mm/year

PARAMETER UTAMA SUMBER

• geometri sumber: panjang-lebar, lokasi • arah dan besar pergerakan

• pengangkatan dan penurunan muka bumi • arah rupture dan cepatnya pergerakan

PARAMETER DASAR: • Bathimetri

• topografi (utk run-up modeling)

DATA CONSTRAINTS ON TSUNAMI MODEL

PARAMETER SEKUNDER:

• Cabang patahan di dekat palung • longsoran di bawah laut

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Indonesia is an earthquake country : Crustal motions from GPS (Bock et al, 2004) India-Australian Plate Eurasian Plate Pacific Plate 5-6 cm/yr 12 cm/yr

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Megathrust earthquake Forearc islands trench Moho

ZONA SUBDUKSI

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Interseismic period

(slow strain accumulation)

Slow uplift

Slow

Submergence

It is like a spring board!

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Co-seismic = earthquake (sudden strain release)

Sudden Uplift

It is like a spring board!

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

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Locking zone

(=seismic zone= zone of strain accum.)

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Tsunami modeling

SOURCE Fault parameters Wave-propagation: F(depth) Shoreline interaction

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

Max. slip 20m

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(Tsunami Research Group Marine Research Center ITB)

Tsunami source base on the Altimetry Data ANIMATION of The 2004 Aceh tsunami

(Hamzah Latief) Vertical displacement of seafloor estimated by Hirata et al. [2005] from satellite altimetry data. ChenJi Ward

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We have used

GPS

records of sea-level change in corals

and satellite imagery

To understand the behavior of the

tsunami source

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Model G

M

_w

9.2

Based on: • Coral Satelite imagery analysis • GPS campaign mode • Continuous GPS (far field) Rupture: • ~1600km long • 10 – 30 meter Displacement westward

(after Chlieh et al, 2005 and

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Courtesy of Mohamed Chlieh

Uplift in 2004

• The greatest uplift

occurred west of the Nicobar islands and southwest of Aceh

Source

parameters

Of

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Mengenal sumber gempa-tsunami

Indonesia

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Gempa Sumatra

(yg paling banyak dipelajari)

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Megathrust earthquake Forearc islands trench

Moho

Sumatran Fault Zone

Sumatran earthquake

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Sumatran fault Zone INDIAN-AUSTRALIAN PLATE EURASIAN PLATE 50 – 60 m m/year Plate moveme nt Jakarta 1881 (7.9) 1941 (7.9) 1797 (M8.4) 1861 (M~8.5) 1907 (~M7.8) 1935 (M7.7) 2000 (M7.8) 2002 1833 (8.9)

2004 (M9.15)

2005 (M 8.7)

_{Currently locked,}

Near end of cycle section

Un known section,

No large eartquakes in Historical records

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Briggs et al.,

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the 2004 earthquake

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the 2005 earthquake

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SIMELUE ISLAND 1861 uplift tsunami 1799 uplift 1400 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)

uplift uplift

Paleoseismic history Simeulue island

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SIMELUE ISLAND 1861 uplift tsunami 1799 uplift 1400 965 uplift uplift Paleoseismic history Simeulue island NW: 400 to 600 year recurrence? SE: 140 to 200 year recurrence? SE Simelue: NW Simelue:

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B at ee fa_u lt A tear in the over-riding plate?

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March 28,2005 Slip on the megathrust B at ee fa_u lt

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Rupture/sumber gempa

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A

A’

uplift subsidence hingeline Ru ptu re z_on e

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A

A’

uplift subsidence hingeline Ru ptu re z_on e

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Near Afulu village, west coast of Nias island January 2005

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Examples from Nias, Simeulue and the Banyak islands

The March 2005 event resulted in impressive uplift …

Old high tide

Old low tide

Old high tide New high tide

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Haloban village, Banyak islands

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A Historical sketch of the 1861 earthquake in Nias

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March 28,2005 Slip on the megathrust B at ee fa_u lt

1861?

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Segmen

Mentawai !!!

Dimana

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Coastlines show subsidence of the Mentawais for many decades

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Evidence for giant earthquakes

in 1797 and 1833

Evidence for giant earthquakes

in 1797 and 1833

Fossil microatolls in the intertidal zone, east coast of North Pagai island

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Years (AD) ~1370 ~1600 1797 & 1833 Paleogeodetic For ~700 years The Mentawai patch appears to be time-predictable and near failure E le v a ti o n r e la ti v e t o m o d e rn s e a l e v e l ( c m )

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SEISMIC

GAP: Before

Aceh-Andaman Earthquake Malaysia S um atr_a

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SEISMIC

GAP: After Aceh_–Andaman

Earthquake Before Nias Earthquake Malaysia S um atr_a

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SEISMIC

GAP: After Nias_Earthquake

Is Mentawai Seismic gap Malaysia S um

atr_a _{How about}

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SuGAr Velocity Field Up to June 2006 Ongoing Post-slip Ongoing Squeezing Of Mentawai

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

Chlieh et al (in review) J Geophys Res

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Photo: Jose Borrero

Padang now

(~800,000 people)

Padang in 1797 (~4,000 people)

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Earthquake and Tsunami Scenarios for

Western part of Sumatra

Patterns of Uplift of the

seafloor produced by the

six megathrust ruptures

scenarios

(Borero et al, 2006)

1797 1833 Scenario 1 Scenario 2 Scenario 3 Scenario 4 D.H. Natawidjaja May 2007

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Animasi proses deformasi gempa dan tsunami Surut dulu Surut dulu Tidak Surut dulu

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Tsunami simulation for an Aceh-2004-like source

Scenario 3: Uplift from 20 m slip on 700-km megathrust rupture

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20-m Slip Scenario in Padang

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20-m Slip Scenario in Bengkulu

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20-m scenario

Turun 0.5 meter

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20-m scenario

Turun 1.5 meter

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Sumber Gempa - Tsunami Jawa

(sedikit tahu, banyak tidaknya)

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SUMARY OF JAVA EARTHQUAKE 1840 – 2005

(modified from Newcomb and McCann, 1987)

• 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

1994 (Pancer)

Time

M 7.8 2006 tsunami M7.8)

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Seismic record for the past 30 years

It lead to a big question…

What is the maximum magnitude of earthquake of the Jawa Subduction zone?

July 2006 (Mw 7.8)

1994 (Mw 7.8)

SEISMIC G_AP

Is it actually less than M8?

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M 7.8

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

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M 7.8

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M 7.8

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M 9.0

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M 9.0

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Historical On-land Earthquakes of Jawa

(Natawidjaja, 2006)

D.H. Natawidjaja May 2007

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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 letusan-letusan 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. ………

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Gempa-Tsunami di Indonesia Timur

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Earthquake and Tsunami of East Indonesia Region

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Earthquakes M>5: 1964-2006 (Engdahl, 2006) < 30 km depth 30 - 60 km

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Recent Earthquake Mw > 7 since 1973

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Historical Earthquake since 1600 (USGS)

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Tsunamigenic earthquake zones and Historical Tsunami

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Historical Tsunami: Year (Run-up in m)

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Historical Tsunami: Year (death)

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Bagaimana dengan tsunami source untuk wilayah Maluku?

M 8 .0

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M 8 .0

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Data from URS

Probability map of tsunami-height hazards in Southeast Asia

Anda percaya ??? Bagaimana kualitas data sumber yang digunakan? Paul Sommervile & Hng Kie Thio

(URS)

Hanya memakai Data seismic dari tahun 1973??

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Concluding remarks

Knowledge of

Earthquake and Tsunami Sources,

Designing

Observation Network and System for

Research and Early Warning System

Public Education and

Community Preparedness

Infrastructure changes, Evacuation plan, and Post-Disaster actions RESEARCH

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