Solomon Islands Earthquake Research Articles

Anisotropic gradients in Iran: Quasi-Love waves illuminate the deep structure and deformation style of the Zagros, Alborz, and Kopet Dagh

We investigate the presence of the quasi-Love wave (qL) at 51 seismic stations of a temporary seismic network across the western Arabia-Eurasia collision zone. We quantify the intensity of the qL observations from the April 12, 2014 Solomon Islands earthquake by calculating the peak-to-peak amplitude ratios of the qL and Love waves, and compare them with predicted qL intensities from previous shear-wave splitting results. We determine the polarity, timing, and period-dependence of the qL observations within the period range of 50–100 s. Our analysis reveals that the qL observations at stations in the Zagros and Alborz mountain belts exhibit opposite characteristics. In contrast to the Alborz stations, the intensity of qL observations at the Zagros stations exhibits relatively negligible dependence on the period, while their receiver-scatterer distances are considerably period-dependent. We approximately locate the anisotropic gradients that generate the qL waves. Our results suggest that a lithospheric gap is responsible for the shallow and abrupt variation in the belt-parallel trend of fast-axis orientations in the westernmost part of the Zagros. Additionally, the period/depth dependence of the anisotropic gradients along the boundary between the central Zagros and central Iran provides insight into the variation in the downward dip of the Arabian lithosphere. The anisotropic gradient located to the north of the Doruneh fault in eastern Iran indicates its role as a major shear zone and lithospheric boundary. Finally, we observe that the spatial distribution of the anisotropic gradient in northeastern Iran matches the higher strain-rate areas in the Kopet Dagh Mountains, suggesting coupling between the lithospheric mantle and crust in that region.

Rock Damage and Aquifer Property Estimation from Water Level Fluctuations in Wells Induced by Seismic Waves: A Case Study in X10 Well, Xinjiang, China

There is a coupling relationship between surrounding rock stress, deformation, and fracture evolution, especially in the microdynamics of the crust caused by mining activities and earthquakes. Previous research has investigated many cases regarding the coseismal water level responses and proposed a method to calculate the aquifer parameters by tidal analysis. However, to date, measurement of the degree of rock damage in the field has not been reported. Quantifying the fracture characteristics is essential for accurate evaluation of rock stability. This study has analyzed the relationship between the seismograms and hydroseismograms in response to the Mw 7.8 Solomon Islands earthquake and the Mw 7.8 Kaikōura earthquake, both events occurring in 2016. The calculated and measured changes in water level in the X10 well were fitted in order to study the relationships among the volumetric strain, the deviatoric strain, and the oscillations in the pore pressure. Then, we further estimate the degree of rock damage and the hydraulic characteristics of the aquifer. The results showed that the values for the rock damage parameter, 0.662 < αD < 0.754, and the Skempton coefficient, −0.100 < A < 0.026, estimated for the Solomon Islands earthquake signified higher damage and dilatancy in the X10 well. Also, the respective values for the parameters, 0.293 < αD < 0.363 and 0.226 < A < 0.251, calculated for the Kaikōura earthquake signified a lower degree of rock damage. It is concluded that the changes in the pore pressure were influenced by both the volumetric strain and the deviatoric strain. The degree of rock damage and the hydraulic properties of the aquifer estimated from the water level fluctuations in the wells which were induced by the seismic waves represent the actual aquifer characteristics.

Composite Megathrust Rupture From Deep Interplate to Trench of the 2016 Solomon Islands Earthquake

AbstractThe deep plate boundary has usually been recognized as an aseismic area, with few large earthquakes occurring at the 60–100 km depth interface. In contrast, we use a finite‐fault rupture model to demonstrate that large slip in the 2016 M7.9 Solomon Islands earthquake may have originated from the deep subduction interface and propagated all the way up to the trench. The initial rupture occurred at a depth of about 100 km, forming a deep asperity and then propagating updip to the middle‐depth large coseismic slip area. Our proposed source model indicates that the depth‐varying rupture characteristics of this event could shift to deeper depths with respect to other subduction zones. This result also implied that the deep subducting plate boundary could also be seismogenic, which might trigger rupture at the typical middle‐depth stress‐locked zone and develop into rare composite megathrust events.

Intraslab rupture triggering megathrust rupture coseismically in the 17 December 2016 Solomon Islands Mw 7.9 earthquake

AbstractThe 17 December 2016 Solomon Islands earthquake (Mw 7.9) initiated ~103 km deep in the subducting Solomon Sea slab near the junction of the Solomon Islands and New Britain trenches. Most aftershocks are located near the Solomon Islands plate boundary megathrust west of Bougainville, where previous large interplate thrust faulting earthquakes occurred in 1995 (Mw 7.7) and 1971 (Mw 8.0). Teleseismic body wave modeling and aftershock relocations indicate that the initial 30 s of the 2016 rupture occurred over depths of 90 to 120 km on an intraslab fault dipping ~30° to the southwest, almost perpendicular to the dipping slab interface. The next 50 s of rupture took place at depths of 32 to 47 km in the deeper (Domain C) portion of the overlying megathrust fault dipping ~35° to the northeast. High susceptibility to triggering in the region accounts for this compound rupture of two separate fault planes.

A Bayesian rupture model of the 2007 Mw 8.1 Solomon Islands earthquake in Southwest Pacific with coral reef displacement measurements

On 1st April 2007 a Mw 8.1 megathrust earthquake occurred in the western Solomon Islands of the Southwest Pacific and generated a regional tsunami with run-up heights of up to 12m. A Bayesian inversion model is constructed to derive fault dip angle and cumulative co-seismic and early post-seismic slip using coral reef displacement measurements, in which both data misfit and moment magnitude are used as constraints. Results show three shallow, high-slip patches concentrated along the trench from west of Ranongga Island to Rendova Island on a fault plane dipping 20°, and a maximum dip slip of 11.6m beneath Ranongga Island. Considerable subsidence on Simbo Island outboard of the trench on the subducting plate is not well explained with this model, but may be related to the effects of afterslip and/or Simbo Island’s location near the triple junction among the Australia, Woodlark and Pacific plates.

Source Models and Near-Field Impact of the 1 April 2007 Solomon Islands Tsunami

Within weeks of the Solomon Islands earthquake of 1 April 2007, international tsunami survey teams discovered important biomarkers of crust rupture and tsunami heights along the islands’ coastlines. Deep-ocean tsunameters recorded the tsunami waves of this event, enabling a real-time inversion of the tsunami source and model evaluation of near-field tsunami impact. The survey measurements provide valuable datasets for further confirmation of the tsunami source of the 1 April 2007 Solomon earthquake. These survey results also aided investigation of the correlation between sources determined by use of tsunameter records and those derived from seismometer records or crust-rupture measurements. In this study, to assess the near-field tsunami impact, we developed tsunami inundation models for the Solomon Islands, including tsunami waveforms, co-seismic land-level changes, and tsunami height distributions on individual islands. Compared with seismic-derived tsunami sources, modeling results based on the tsunameter-derived tsunami sources were a good match with field survey measurements. These results highlight the accuracy and efficiency of the tsunameter-derived tsunami source in modeling the near-field tsunami impact along a complex archipelago. We show that the source models, although derived by use of different methods, are all suited to initiation of inundation models developed for Solomon Islands. As these source models become available in real time or near real time, they can be implemented immediately in the inundation models to provide rapid guidance on tsunami hazard assessment, focused search and rescue operations, and post-event recovery and reconstruction.

Earth's free oscillations recorded by free-fall OBS ocean-bottom seismometers at the Lesser Antilles subduction zone

Three unburied ocean bottom seismometers (OBS) equipped with Trillium 240 s broad-band seismometers recorded spheroidal free oscillations of the Earth out to periods over 1000 s period, for the M = 8.1, April 1, 2007 Solomon Islands earthquake. In contrast to broadband observatories of the global network that operate in quiet continental locations, these instruments were dropped on the several-km thick layer of sediments of the forearc and accretionary wedge of the Lesser Antilles subduction zone. Furthermore, a high ambient noise level due to the ocean surface infragravity waves is expected to cover the frequency band of Earth's normal modes band when recorded at these sites. In spite of these hostile environmental conditions, the frequency of clearly defined peaks of the Earth's normal modes were measured after the earthquake. This suggests that the recording of normal modes and long period waves can be extended to parts of the hitherto inaccessible ocean with currently available OBS technology.

High‐resolution locations of triggered earthquakes and tomographic imaging of Kilauea Volcano's south flank

The spatiotemporal patterns of seismicity beneath Kilauea's south flank give insight to the structure and geometry of the decollement on which large, tsunamigenic earthquakes have occurred, and its relation to slow slip events (SSEs), which have been observed every 1 to 2 years since 1997. In order to record earthquakes triggered by a SSE that was predicted to occur in March 2007, a temporary network of 20 seismometers was deployed on Kilauea's south flank, termed the SEQ network. While the SSE did not occur until 17 June 2007, theSEQ network recorded over 3000 earthquakes, including those triggered by the SSE. We relocate hypocenters of volcano‐tectonic earthquakes and invert for P and S wave velocity structure using waveform cross‐correlation and double‐difference tomography using data from the SEQ network and the permanent Hawaii Volcano Observatory network (HVO) data, with additional data from other previous temporary arrays. The best‐constrained hypocenters, recorded by both the SEQ and HVO networks, indicate the decollement as a subhorizontal layer of seismicity at 8 km depth less than 1 km thick in most areas, with the western portion of the decollement dipping to the southeast. The seismicity triggered by the June 2007 SSE includes over 400 earthquakes overlapping with the southern edge of the decollement seismicity. A shallower swarm of earthquakes also occurred between 2 and 7 km depth in April 2007 near Apua Point, and may have been indirectly triggered by the Mw 8.1 Solomon Islands earthquake at ∼6000 km distance, which occurred 48 h prior to the beginning of the swarm.

Slip distribution from the 1 April 2007 Solomon Islands earthquake: A unique image of near‐trench rupture

We estimate the slip distribution from the MW 8.1 Solomon Islands earthquake in 2007, from two post‐seismic surveys measuring uplifted coral and submerged coastal features. The occurrence of islands extremely proximal to the trench and nucleation of rupture allowed for the collection of unprecedented coseismic deformation dataset along a large megathrust earthquake. Using data from the two surveys along the southeastern half of the slip zone within five weeks of the event, we model the elastic dislocation to identify the optimal (29°), and alternate (20°), dip and distribution of thrust along the southern rupture. The vertical deformation, which includes both coseismic and early postseismic deformation, has highly variable and large slip within 25 km of the trench and straddling Ranongga Island. The shallow focus of slip in the near‐trench area may explain the locally high tsunami run‐up on portions of Simbo Island, however the aseismic contribution of afterslip remains unknown.

The Effect of the Great Barrier Reef on the Propagation of the 2007 Solomon Islands Tsunami Recorded in Northeastern Australia

The effect of offshore coral reefs on the impact from a tsunami remains controversial. For example, field surveys after the 2004 Indian Ocean tsunami indicate that the energy of the tsunami was reduced by natural coral reef barriers in Sri Lanka, but there was no indication that coral reefs off Banda Aceh, Indonesia had any effect on the tsunami. In this paper, we investigate whether the Great Barrier Reef (GBR) offshore Queensland, Australia, may have weakened the tsunami impact from the 2007 Solomon Islands earthquake. The fault slip distribution of the 2007 Solomon Islands earthquake was firstly obtained by teleseismic inversion. The tsunami was then propagated to shallow water just offshore the coast by solving the linear shallow water equations using a staggered grid finite-difference method. We used a relatively high resolution (approximately 250 m) bathymetric grid for the region just off the coast containing the reef. The tsunami waveforms recorded at tide gauge stations along the Australian coast were then compared to the results from the tsunami simulation when using both the realistic 250 m resolution bathymetry and with two grids having fictitious bathymetry: One in which the the GBR has been replaced by a smooth interpolation from depths outside the GBR to the coast (the “No GBR” grid), and one in which the GBR has been replaced by a flat plane at a depth equal to the mean water depth of the GBR (the “Average GBR” grid). From the comparison between the synthetic waveforms both with and without the Great Barrier Reef, we found that the Great Barrier Reef significantly weakened the tsunami impact. According to our model, the coral reefs delayed the tsunami arrival time by 5–10 minutes, decreased the amplitude of the first tsunami pulse to half or less, and lengthened the period of the tsunami.

Shoreline changes and vertical displacement of the 2 April 2007 Solomon Islands earthquake Mw 8.1 revealed by ALOS PALSAR images

The Solomon Islands earthquake with magnitude Mw = 8.1 occurred on 2 April 2007 at 7:39 local time. We used six L-band Synthetic Aperture Radar (SAR) images acquired by the Advanced Land Observing Satellite (ALOS) Array L-band Synthetic Aperture Radar (PALSAR) data to roughly estimate the shoreline and vertical displacements associated with this earthquake. We processed the raw SAR data with the SIGMA-SAR software package, produced by Japan Aerospace Exploration Agency (JAXA). Our measurements showed good agreement with field observations performed by Japanese scientists just a few weeks after the earthquake. We estimated the dislocation related to this earthquake between Ranongga Island and Simbo Island. Moreover, we compared the radar imagery analysis data with Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data and found that the SAR images were more efficient for investigating vertical displacements than similar techniques based on data from optical sensors. Measurements of offset cross-correlation intensities in SAR images indicated about 1.4 m of uplift on southwestern New Georgia Island.

Solomon Islands Tsunami, One Year Later

The geologic and economic effects of the 2 April 2007 Solomon Islands earthquake and tsunami are distinctly visible a little more than a year after the event. Coral reef colonies that were sheared off and uplifted are slowly recovering, and many new earthquake‐triggered landslides remain mobile. Large volumes of sediment created by the earthquake and mobilized by the tsunami have been flushed from the lagoons between the reef and shoreline into deeper water, although significant quantities remain on land. Sediment from the lagoons covers piles of shattered coral that the tsunami moved from the lagoons to the base of channels in the barrier reef. These shattered corals have a higher chance of preservation as paleotsunami deposits than the material deposited on land.

Developing A Method For Tsunami Damage Detection Using High-Resolution Optical Satellite Imagery

The authors propose a method to detect the structural damage due to tsunami inundation flow, by using the visual interpretation and analysis of high-resolution optical satellite imagery. The method is implemented to the recent tsunami event, the 2007 Solomon Islands earthquake tsunami, to identify the damage probabilities within the inundation zone and construct the fragility function (damage probability to tsunami height), combined with the post-tsunami survey data.

Field Survey and Numerical Simulation on 2007 Solomon Islands Earthquake Tsunami

The Solomon Islands Earthquake Tsunami was generated by a big earthquake of M8.1 on 2 April 2007, and caused severe damages particularly in western islands of the Solomon Islands, resulting in the death toll of 52. To understand tsunami characteristics and damages, a field survey was conducted. Measured tsunami inundation height was approximately 4-5 m at the north part of Simbo Island and at the south coast of Ghizo Island. Human losses were, however, mitigated by residents' evacuation to hills and high-floored houses soon after the earthquake occurrenceand as soon as they watched the tsunami travelling in the offshore. Numerical simulations were also conducted to estimate and understand the tsunami. The effect of reefs in coastal areas was additionally investigated from the numerical simulations.

Dispersion of Rayleigh Waves across Australia

Summury The history of seismological investigations of Australian crustal structure is outlined. New measurements have been made of phase and group velocities of Rayleigh waves for a number of continental paths. The most extensive empirical dispersion curve comes from a Solomon Islands earthquake which lies near a great circle through the Charters Towers and Perth observatories. This curve is in general agreement with published values for the Canadian Shield. It indicates a mean crustal thickness between 30 and 35 km. Some variation in crustal properties is indicated towards the northwest. The average crust under the Coral Sea may be 30 per cent thinner than that under the continent. In this paper measurements of dispersion in Rayleigh waves recorded at Brisbane, Charters Towers and Perth seismological observatories are presented. Comparison of these data with similar measurements for the Canadian Shield and with theoretical dispersion curves provides fresh evidence on the structure of the Australian continental crust. Broadly, the continent may be divided into three main geological provinces (cf. Bureau of Mineral Resources, 1960). The great Pre-Cambrian Shield, with

Crustal structure and surface-wave dispersion. part II Solomon Islands earthquake of July 29, 1950*

Abstract Rayleigh waves from the Solomon Islands earthquake of July 29, 1950, recorded at Honolulu, Berkeley, Tucson, and Palisades are analyzed. Both the direct waves and those propagated through the Antipodes were observed for all stations except Honolulu. Application of a correction for land travel results in a dispersion curve for the oceanic portion of the path. It is found that the observed dispersion could be accounted for by propagation through a layer of water 5.57 km. thick overlying simatic rocks having shear velocity 4.56 km/sec. and density 3.0 gm/cc. Basement structure in the Pacific, Indian, South Atlantic, and North Atlantic oceans is ideptical within the limits of accuracy of the method. The sinusoidal nature and duration of the coda is explained by the effect of the oceans on the propagation of Rayleigh waves. The results are compatible with seismic refraction measurements in the Atlantic and Pacific oceans.