(T1.5-P29)

Hidayanti

Meteorological Climatological and Geophysical Agency of Indonesia (BMKG)

Abstract

The 1921 earthquake was occurred in the Java trench and located between two

tsunami earthquake of 1994 (Banyuwangi) and 2006 (Pangandaran) south of

Java. The 1921 earthquake also generate tsunami that recorded in tide gauge

of Cilacap with maximum height of tsunami is around 10 cm. From paleo

tsunami study we found the tsunami deposit of the 1921 earthquake in around

of Prigi beach. We suppose that the 1921 earthquake have strike-slip type for

the source mechanism. We perform the numerical tsunami simulation to

estimate the source of the 1921 earthquake. We used the tide gauge data from

Cilacap and also tsunami deposit data in Cilacap, Yogyakarta, and Banyuwangi

to validation the tsunami model. We estimate the fault length was 72 km and

width was 30 km.

1. Introduction

Indonesian archipelagos and its surrounding is one of the most seismically

active regions in the world and has very complicated plate convergence. The

complexity of tectonic feature is still less known quantitatively on the natural of

earthquake and their accompanying tsunamis.

At the Pangandaran earthquake in 2006 , a form of interaction that occurs plate

is a form of convergence in the form of a subduction. subduction can occurs

when dense oceanic plates collide with a mass greater continental plates are

thicker and more stable but small mass meeting.

History recorded earthquake in Java mentioned in the interval 1833-2003 has

occurred 68 times the destructive earthquake category (BMKG). In 1859 an

earthquake in Pacitan with estimates above 7 SR . Then in Yogyakarta been a

big earthquake that killed over 500 people in 1867. And the two last major

quake was the Yogyakarta earthquake in May 2006 and a magnitude 6.3

earthquake and Pangandaran in July 2006 with a magnitude of 6.8 magnitude

with its epicenter is adjacent by the earthquake that occurred in 1921 .

On 11 September 1921 at 11.00 am , there was a strong earthquake with

epicenter in the Indian Ocean south of Java . Coordinates of the epicenter and

magnitude earthquake , according to Gutenberg and Richter (1954 ) is located

at the coordinates 11 ° S - 111 ° E with a force M = 7.5 on the Richter scale .

The Inundation modeling was simulated using modified TUNAMI-N2 (Tohoku

University’s Numerical Analysis Model for Investigation Field Tsunami, No. 2).

2. Data and Methods

2.1 Tsunami Simulation, Bathymetry, and Topography Data

We used tsunami simulation code which is developed by Yanagisawa (2012)

based on the TUNAMI-N2 in nested grid system. We applied nonlinear shallow

water theory with bottom friction in the form of Manning’s formula. Bathymetry

and topography data for the first to third region are taken from the General

Bathymetric Chart of the Ocean (GEBCO) 30 arc-second (resampling to 1 min

grid size). Bathymetry and topography for the fourth region are interpolated from

Shuttle Radar Topographic Mission (SRTM). We divided become 4 region for

tsunami simulation area, there are Region 1, Region 2, Region 3, and Region 4

with resolution 1’, 20”, 6.6667”, and 2.2222” respectively. We also used tsunami

record in Cilacap for validation.

We used single fault plane to calculate tsunami simulation with length 72 km

and width 30 km. We applied parameter of source mechanism from Emile A.

Okal (2012).

2.2 Paleo tsunami data

Previously, BMKG collborate with Bandung Institute of Technology (ITB) have

research paleo tsunami in south coast of Java. And in Prigi beach (East Java)

found tsunami suspect of the 1921, Java earthquake.

a. b.

Figure 1. Epicenter of the 11 September 1921 earthquake (red star) based on

Gutenberg and Richter (1954)

Figure 2. a. Tsunami simulation area in this study; b. Tsunami record in Cilacap

(Solo’ev and Go, 1954)

Figure 3. Seismic record and focal mechanism of Java earthquake, 1921

(Emile A. Okal, 2012)

Figure 4. a. Location of tsunami suspect in Prigi beach (East Java); b. Tsunami

suspect in Prigi beach

3. Results

4. References

Emile A. Okal. 2012. The south of Java Earthquake of 1921 September 11 : a

negative search for a large interplate thrust event at the Java Trench.

Geophysical Journal International

Solov’ev, S.L. & Go, Ch. N., 1984. Catalogue of tsunamis on the Western shore

of the Pacific Ocean, Can. Transl. Fish. Aquat. Sci., 5077, 439pp.

Nurashid, Nur Intan. 2013. Tsunami Inundation Modeling Along the East Coast

of Sabah, Malaysia for Potential Earthquakes in Sulu Sea. Bulletin of

IISEE. Japan.

Figure 5. a. Deformation of the 1921 Java earthquake; b. Maximum height of

tsunami simulation for the 1921 Java earthquake

a.

b.

Source : Paleo Tsunami

Team of BMKG and ITB

a. b.

mete

rm

ete

r

Observation dataSynthetic data

Location of Tsunami

Suspect

a. b.

c.

Figure 6. a. Snapshot tsunami propagation of the 1921 Java earthquake; b.

Comparison observation and synthetic data; c. Inundation map in Prigi beach

and surroundings area