Java Tsunami Earthquake Research Articles

Marine forearc structure of eastern Java and its role in the 1994 Java tsunami earthquake

Abstract. We resolve a previously unrecognized shallow subducting seamount from a re-processed multichannel seismic profile crossing the 1994 Mw 7.8 Java tsunami earthquake rupture area. Seamount subduction occurs where the overriding plate experiences uplift by lateral shortening and vertical thickening. Pronounced back-thrusting at the landward slope of the forearc high and the formation of splay faults branching off the landward flank of the subducting seamount are observed. The location of the seamount in relation to the 1994 earthquake hypocentre and its co-seismic slip model suggests that the seamount acted as a seismic barrier to the up-dip co-seismic rupture propagation of this moderate-size earthquake.

Long and Short Wavelength of Geodetic Strain Rate Tapering Earthquake Potential in Western Java

Shallow earthquake produced by intra-island fault in a populated region could be a catastrophic disaster. Java island is the most populated area specifically in Western Java since there include Jakarta, the capital city of Indonesia. Cimandiri, Lembang and Baribis fault as main intra-island fault are considered to be responsible due to some shallow historical earthquake in Western Java. However, convergent plate margin such as Java Island generates a broad spectrum of deformation pattern that potentially distracts the deformation due to Baribis fault. In addition, slow relative motion of Sunda block and postseismic deformation due to the 2006 Java tsunami earthquake involve along those fault. Here, we intend to conduct a wavelength decomposition of strain rate calculated from GNSS (Global Navigation Satellite System) data. We expect to separate long wavelength due to wider-region deformation such as deformation due to the interacting plate and postseismic deformation to obtain Short wavelength due to each fault. We utilized the daily position of recent continuous geodetic data to produce strain rate. Therefore, we could apply a moving average filter to extract a short wavelength component. We obtained long wavelength (-150 to 150 nanostrain/yr) in Western Java shows extension indicating the postseismic effect is still continuous while short wavelength (-75 to 75 nanostrain/yr) varies in space.

Present-day crustal deformation revealed active tectonics in Yogyakarta, Indonesia inferred from GPS observations

We investigated the active crustal structure in Yogyakarta, Indonesia, using new and denser Global Positioning System (GPS) data. Deformation rate estimated from five years (2013–2018) of observations on 22 campaign might record broad deformation after the 2006 Mw7.8 Java tsunami earthquake and postseismic transient due to the 2006 Mw6.3 Yogyakarta earthquake. We conducted a decomposition method to obtain a short wavelength feature by removing those postseismic deformations from the observation data. The short wavelength pattern revealed active tectonics indicating a combination of E–W dip-slip motion and N–S left-lateral structure. A large maximum shear strain rate (>0.1 microstrain/yr) was estimated along the Opak fault while a large dilatation rate (<-0.1 microstrain/yr) was estimated around the Bantul Graben. The analysis result indicates important implications for crustal dynamics and assessing future seismic hazards potential in the Yogyakarta region.

Active tectonic deformation in Java, Indonesia inferred from a GPS-derived strain rate

We investigated the active tectonic deformation in Java using Global Positioning System (GPS) velocity data from 2008 to 2013. We calculated strain rate and estimate that, in general, Java experiences a large strain rate (> 1 microstrain/yr) with an extensional strain (∼5 microstrain/yr) associated with the ongoing postseismic deformation of the 2006 Java tsunami earthquake. A large compressional dilatation rate fault zone (< -3 microstrain/yr) was estimated along the Cimandiri and Cipamingkis faults in West Java, Jakarta fault in Jakarta, Kendeng fault extending from Central Java to the east up to the Madura Strait, and volcanic activity in Banten and Yogyakarta. A large maximum shear strain rate (> 1 microstrain/yr) was estimated along the Wongsorejo and the Montong faults in East Java, and the Lasem fault in Central Java. We show that our strain rate estimation is able to identify active tectonic regions in Java.

Rupture evolution of the 2006 Java tsunami earthquake and the possible role of splay faults

The 2006 Mw 7.8 Java earthquake was a tsunami earthquake, exhibiting frequency-dependent seismic radiation along strike. High-frequency global back-projection results suggest two distinct rupture stages. The first stage lasted ∼65s with a rupture speed of ∼1.2km/s, while the second stage lasted from ∼65 to 150s with a rupture speed of ∼2.7km/s. High-frequency radiators resolved with back-projection during the second stage spatially correlate with splay fault traces mapped from residual free-air gravity anomalies. These splay faults also colocate with a major tsunami source associated with the earthquake inferred from tsunami first-crest back-propagation simulation. These correlations suggest that the splay faults may have been reactivated during the Java earthquake, as has been proposed for other tsunamigenic earthquakes, such as the 1944 Mw 8.1 Tonankai earthquake in the Nankai Trough.

Effect of coseismic and postseismic deformation on homogeneous and layered half-space and spherical analysis: Model simulation of the 2006 Java, Indonesia, tsunami earthquake

Abstract We simulate surface displacements calculated on homogeneous and layered half-space and spherical models as applied to the coseismic and postseismic (afterslip and viscoelastic relaxation) of the 2006 Java tsunami earthquake. Our analysis of coseismic and afterslip deformation suggests that the homogeneous half-space model generates a much broader displacement effect than the layered half-space and spherical models. Also, though the result for surface displacements is similar for the layered half-space and spherical models, noticeable displacements still occurred on top of the coseismic fault patches. Our displacement result in afterslip modeling suggests that significant displacements occurred on top of the main afterslip fault patches, differing from the viscoelastic relaxation model, which has displacements in the front region of coseismic fault patches. We propose this characteristic as one of the important features differentiating a postseismic deformation signal from afterslip and viscoelastic relaxation detected by geodetic data.

Long aseismic slip duration of the 2006 Java tsunami earthquake based on GPS data

The Java earthquake occurred on July 17, 2006 with magnitude 7.8 associated to the subduction process of Indo-Australian plate and Sundaland block off southwestern coast of Java. We present postseismic deformation parameters of the 2006 Java earthquake analyzed using campaign GPS observation from 2006 to 2008 and continuous observation from 2007 to 2014. We use an analytical approach of logarithmic and exponential functions to model these GPS data. We find that the decay time in the order of hundreds of days after the mainshock as observed by 8 years’ data after the mainshock for magnitude 7 earthquake is longer than a general megathrust earthquake event. Our findings suggest that the 2006 Java earthquake which is considered as “tsunami earthquake” most probably occurred in the region that has low rigidity and tends to continuously slip for long time periods.

Investigation of the best coseismic fault model of the 2006 Java tsunami earthquake based on mechanisms of postseismic deformation

We investigate three available coseismic fault models of the 2006 M7.8 Java tsunami earthquake, as reported by Fujii and Satake (2006), Bilek and Engdahl (2007), and Yagi and Fukahata (2011), in order to find the best coseismic model based on mechanisms of postseismic deformation associated with viscoelastic relaxation and afterslip. We construct a preliminary rheological model using vertical data, obtaining a final rheological model after we include horizontal and vertical components of afterslip in the further process. Our analysis indicates that the coseismic fault model of Fujii and Satake (2006) provides a better and more realistic result for a rheological model than the others. The best-fit rheological model calculated using the coseismic fault model of Fujii and Satake (2006) comprises a 60±5km elastic layer thickness with a viscosity of 2.0±1.0×1017Pas in the asthenosphere. Also, we find that afterslip is dominant over the horizontal displacements, while viscoelastic relaxation is dominant over the vertical displacement. Additionally, in comparison to the coseismic displacement found through GPS data taken at BAKO station, our calculation indicates that Fujii and Satake (2006) modeled coseismic displacements with less GPS data misfit than the other examined models. Finally, we emphasize that our methodology for evaluating the best coseismic fault model can satisfactorily explain the postseismic deformation of the 2006 Java tsunami earthquake.

Tsunami Hazard Mitigation at Palabuhanratu, Indonesia

Several large earthquakes have recently occurred along the Sumatra-Java subduction zone, the 2004 great Sumatra-Andaman earthquake, the 2005 great Nias earthquake, the 2006 West Java tsunami earthquake, the 2007 great Bengkulu earthquake, and the 2010Mentawai tsunami earthquakes. Serious tsunami disasters were caused by the great underthrust earthquakes which ruptured the plate interface near the trench such as the 2004 Sumatra-Andaman, 2006West Java, 2010Mentawai earthquakes. At Palabuhanratu, maximum tsunami height distribution and inundation areas were computed from expected fault models located near the Java trench. The results shows that the most populated areas of Palabuhanratu would be severely damaged by the expected tsunami caused by the fault model of Mw 8.5. After discussing tsunami disaster mitigation measures with the local government, the result of tsunami inundation area in this study were used to decide tsunami evacuation areas and evacuation routes. The local government also installed tsunami evacuation sign boards near the coast.

The 25 October 2010 Mentawai tsunami earthquake (Mw7.8) and the tsunami hazard presented by shallow megathrust ruptures

The 25 October 2010 Mentawai, Indonesia earthquake (M_w 7.8) ruptured the shallow portion of the subduction zone seaward of the Mentawai islands, off-shore of Sumatra, generating 3 to 9 m tsunami run-up along southwestern coasts of the Pagai Islands that took at least 431 lives. Analyses of teleseismic P, SH and Rayleigh waves for finite-fault source rupture characteristics indicate ∼90 s rupture duration with a low rupture velocity of ∼1.5 km/s on the 10° dipping megathrust, with total slip of 2–4 m over an ∼100 km long source region. The seismic moment-scaled energy release is 1.4 × 10^(−6), lower than 2.4 × 10^(−6) found for the 17 July 2006 Java tsunami earthquake (M_w 7.8). The Mentawai event ruptured up-dip of the slip region of the 12 September 2007 Kepulauan earthquake (M_w 7.9), and together with the 4 January 1907 (M 7.6) tsunami earthquake located seaward of Simeulue Island to the northwest along the arc, demonstrates the significant tsunami generation potential for shallow megathrust ruptures in regions up-dip of great underthrusting events in Indonesia and elsewhere.

Anatomy of the western Java plate interface from depth-migrated seismic images

Newly pre-stack depth-migrated seismic images resolve the structural details of the western Java forearc and plate interface. The structural segmentation of the forearc into discrete mechanical domains correlates with distinct deformation styles. Approximately 2/3 of the trench sediment fill is detached and incorporated into frontal prism imbricates, while the floor sequence is underthrust beneath the decollement. Western Java, however, differs markedly from margins such as Nankai or Barbados, where a uniform, continuous decollement reflector has been imaged. In our study area, the plate interface reveals a spatially irregular, nonlinear pattern characterized by the morphological relief of subducted seamounts and thicker than average patches of underthrust sediment. The underthrust sediment is associated with a low velocity zone as determined from wide-angle data. Active underplating is not resolved, but likely contributes to the uplift of the large bivergent wedge that constitutes the forearc high. Our profile is located 100 km west of the 2006 Java tsunami earthquake. The heterogeneous decollement zone regulates the friction behavior of the shallow subduction environment where the earthquake occurred. The alternating pattern of enhanced frictional contact zones associated with oceanic basement relief and weak material patches of underthrust sediment influences seismic coupling and possibly contributed to the heterogeneous slip distribution. Our seismic images resolve a steeply dipping splay fault, which originates at the decollement and terminates at the sea floor and which potentially contributes to tsunami generation during co-seismic activity.

CRUSTAL DEFORMATION STUDIES IN JAVA (INDONESIA) USING GPS

Along the Java trench the Australian–Oceanic plate is moving and pushing onto and subducting beneath the Java continental crust at a relative motion of about 70 mm/yr in NNE direction. This subduction-zone process imposed tectonic stresses on the fore-arc region offshore and on the land of Java, thus causing the formation of earthquake fault zones to accommodate the plate movement. Historically, several large earthquakes happened in Java, including West Java. This research use GPS surveys method to study the inter-seismic deformation of three active faults in West Java region (i.e. Cimandiri, Lembang and Baribis faults), and the co-seismic and post-seismic deformation related to the May 2006 Yogyakarta and the July 2006 South Java earthquakes.Based on GPS surveys results it was found that the area around Cimandiri, Lembang and Baribis fault zones have the horizontal displacements of about 1 to 2 cm/yr or less. Further research is however still needed to extract the real inter-seismic deformation of the faults from those GPS-derived displacements. GPS surveys have also estimated that the May 2006 Yogyakarta earthquake was caused by the sinistral movement of the (Opak) fault with horizontal co-seismic deformation that generally was less than 10 cm. The post-seismic horizontal deformation of the July 2006 South Java tsunami earthquake has also been estimated using GPS surveys data. In the first year after the earthquake (2006 to 2007), the post-seismic deformation is generally less than 5 cm; and it becomes generally less than 3 cm in the second year (2007 to 2008).

Waveform inversion for slip distribution of the 2006 Java tsunami earthquake by using 2.5D finite-difference Green’s function

Abstract We first incorporate the large effect of near-source heterogeneity on teleseismic body waveforms in the inversion of the slip distribution of the 2006 Java tsunami earthquake. We incorporate the effect by computing the response of an assumed “2.5D” model structure of the Java trench by a 2.5D finite-difference method. Based on a simulation of inversion, we suggest that intense smearing is possible when we apply 1D Green’s functions in the analysis, and that it may obscure the slip pattern. In the inversion of real data, we confirm macroscopic features, such as a long duration (∼ 165 s) and a slow rupture velocity (∼ 1.25 km/s). The region of the initial rupture is found to be isolated from the eastern broad region in which we further identify a heterogeneous slip distribution. Most of these regions are likely to be at the sedimentary plate interface where the accreted sediment and the subducting plate are in contact. In particular, the nearly “isolated” feature of a shallow slip region suggests a possible faulting in the shallowest part of the sedimentary plate interface without being strongly enforced by the rupture propagated from the deeper part of the fault. Such heterogeneity suggests a highly variable frictional behavior at the sedimentary plate interface.

The 17 July 2006 Java tsunami earthquake

The 17 July 2006 Java earthquake involved thrust faulting in the Java trench and excited a deadly tsunami (∼5–8 m) that inundated the southern coast of Java. The earthquake's size estimates vary significantly with seismic wave period: very long‐period signals (300–500+ s) indicate a seismic moment of 6.7 × 1020 Nm (Mw = 7.8), MS (∼20 s) = 7.2, mb (∼1 s) = 6.2, while shaking intensities (3–10 Hz) were ≤ MMIV. The large tsunami relative to MS characterizes this event as a tsunami earthquake. Like previous tsunami earthquakes, the Java event had an unusually low rupture speed of 1.0–1.5 km/s, and occurred near the up‐dip edge of the subduction zone thrust fault. Most large aftershocks involved normal faulting. The rupture propagated ∼200 km along the trench, with several pulses of shorter period seismic radiation superimposed on a smooth background rupture with an overall duration of ∼185 s.

The 1994 Java Tsunami earthquake and its “Normal” aftershocks

We compare the source spectra of the 1994 Java tsunami earthquake (MW = 7.9) and its two largest aftershocks. The source spectra of the aftershocks, from teleseismic P‐waves, can be fit remarkably well by a standard ω2 model. However, the mainshock shows a lower moment release at periods of 1–20 sec than its aftershocks, although its total moment is 1000 times larger. We analyze this discrepancy by exploring two mechanisms that, in a simple Haskell rupture model, will decrease one of the corner frequencies of the source spectrum: 1. lowering the rupture velocity and 2. lowering the particle (slip) velocity. Both changes maintain an identical spectral drop‐off and static stress drop, and result in the characteristic spectral shape of a “slow” earthquake. These kinematic models can be related to physical rupture parameters by considering the earthquake energy budget. In both cases the radiated seismic energy is lowered, either due to a higher frictional stress during the break‐down phase, increasing the fracture energy (case 1), or by an increase in the sliding stress (case 2). We do not suggest that either of these simplified models is the only possible interpretation, but want to illustrate the danger in directly interpreting “slow” earthquakes as having a low rupture velocity.

The 1994 Java tsunami earthquake: Slip over a subducting seamount

On June 2, 1994, a large subduction thrust earthquake (Ms 7.2) produced a devastating tsunami on the island of Java. This earthquake had a number of unusual characteristics. It was the first recorded large thrust earthquake on the Java subduction zone. All of the aftershock mechanisms exhibit normal faulting; no mechanisms are similar to the main shock. Also, the large tsunami and the relatively low energy radiated by the main shock have led to suggestions that this earthquake might have involved slow, shallow rupture near the trench, similar to the 1992 Nicaragua earthquake. We first relocate the main shock and the aftershocks. We then invert long‐period surface waves and broadband body waves to determine the depth and spatial distribution of the main shock slip. A dip of 12°, hypocenter depth of 16 km and moment of 3.5×l020 N m (Mw 7.6) give the best fit to the combined seismic data and are consistent with the plate interface geometry. The source spectrum obtained from both body and surface waves has a single corner frequency (between 10 and 20 mHz) implying a stress drop of ∼0.3 MPa. The main energy release was preceded by a small subevent lasting ∼12 s. The main slip occurred at ∼20 km depth, downdip and to the NW of the hypocenter. This area of slip is collocated with a prominent high in the bathymetry that has been identified as a subducting seamount. We interpret the Java earthquake as slip over this subducting seamount, which is a locked patch in an otherwise decoupled subduction zone. We find no evidence for slow, shallow rupture. No thrust aftershocks are expected if the entire locked zone slipped during the main shock, but extension of the subducting plate behind the seamount would promote normal faulting as observed. It seems probable that such a source model could also explain the size and timing of the observed tsunami.