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We estimated the slip distribution on the fault of the 2005 Nias earthquake (M w 8.6) by inversions of local GPS and coastal uplift/subsidence data and tsunami waveform data. The 2005 Nias earthquake occurred approximately three months after the 2004 Sumatra–Andaman earthquake (M w 9.1) at the southern extension off Sumatra Island, Indonesia. The tsunami from the 2005 earthquake caused significantly less damage than the 2004 tsunami, yet was recorded at tide gauges and ocean bottom pressure gauges around the Indian Ocean, including the coasts of Africa and Antarctica. The elastic and gravitational coupling between the solid earth and the ocean causes not only a traveltime delay but also the change of waveforms of far-field tsunamis relative to the prediction based on the long-wave theory. We corrected the computed tsunami Green's functions for the elastic and gravitational coupling effect in the tsunami waveform inversion. We found a diffused slip (∼2 m over an area of 400 km × 100 km) at deeper parts (20–54 km) of the fault with a large localized slip (7 m over 100 km × 100 km) slightly south of the epicentre. The large slips at deeper parts of the fault were responsible for the small tsunami generation. Inversion using far-field tsunami data yielded a slip distribution similar to that obtained using local geodetic data alone and that from the joint inversion of local geodetic and far-field tsunami data, which is also similar to slip distributions from previous studies based on local geodetic data. This demonstrates that far-field tsunami waveforms, once corrected for propagation effects, can be used to estimate the slip distribution of large submarine earthquakes leading to results that are similar to those obtained using sparse local geodetic data. [ABSTRACT FROM AUTHOR]

In this paper, we compare two different methods for group velocity inversion: iterative, least-squares subspace optimization and probabilistic sampling based on the transdimensional (Trans-D) Bayesian method with tree-based wavelet parametrization. The wavelet parametrization used a hierarchical prior for wavelet coefficients which could adapt to the data. We applied these inversion methods for ambient noise tomography of the western part of Java, Indonesia. This area is an area prone to multiple geological hazards due to its proximity to the subduction of the Australia Plate beneath Eurasia. It is therefore important to have a better understanding of upper crustal structure to support seismic hazard and disaster mitigation efforts in this area. We utilized a new waveform data set collected from 85 temporary seismometers deployed during 2016–2018. Cross-correlation of the waveform data was applied to retrieve empirical Rayleigh wave Green's functions between station pairs, and the spatial distribution of group velocity was obtained by inverting dispersion curves. Our results show that, although computationally expensive, the Trans-D Bayesian approach offered important advantages over optimization, including more effective explorative of the model space and more robust characterization of the spatial pattern of Rayleigh wave group velocity. Meanwhile, the iterative, least-square subspace optimization suffered from the subjectivity of choice for reference velocity model and regularization parameter values. Our Rayleigh wave group velocity results show that for short (1–10 s) periods group velocity correlates well with surface geology, and for longer periods (13–25 s) it correlates with centres of volcanic activity. [ABSTRACT FROM AUTHOR]

Highlights from the article: On 28 September 2018, an M SB W sb 7.5 earthquake struck Palu, Indonesia, and caused a large number of deaths and economic losses. Seismic moment tensor solutions determined by different institutes consistently suggest that this earthquake is overall a strike-slip event. An InSAR automated processing environment, gInSAR [6] was applied to conduct the InSAR processing and a 30-m-resolution SRTM data was used in the processing. From co-seismic InSAR deformation data, it is clear that multiple segments were ruptured during the earthquake.

Abstract: The technique to retrieve Green’s functions by cross-correlation of seismic noise that is now often referred to as seismic interferometry opened the way to a completely new type of seismological observation – the continuous monitoring of changes in the subsurface medium. In this paper we review Passive image interferometry (PII) as the technique that makes use of the possibility to repeatedly retrieve Green’s functions in order to precisely infer medium changes by comparing Green’s functions that are retrieved at different times. PII is capable of identifying velocity changes below 0.1% and was applied successfully in different tectonic situations. We review three investigations of PII that demonstrate the wide range of possible applications. The first application that introduced the concept of PII in 2006 revealed hydrology related changes of subsurface velocity at Merapi volcano. The second application we present was the first noise based observation of co-seismic changes. And we finally review a recent investigation that documented velocity variations in the shallow subsurface of the moon. [Copyright &y& Elsevier]

Empirical green's function (EGF) analysis has remained little used to image the rupture properties of the giant 26 December 2004 Sumatra earthquake. The 2 November 2002 foreshock (Mw 7.2), close to the mainshock epicenter, gives us the opportunity to use its waveforms to empirically simulate the Rayleigh-wave propagation of the Sumatra earthquake. We first show that the exceptional size of the Sumatra earthquake does not prevent use of the EGF technique. Four aftershocks (Mw 5.9-6.1), distributed along the Sumatra--Andaman trench, are shown to have consistent Rayleigh waves for periods between 100 and 200 sec. At a lower frequency, we present two large earthquakes of the Mexican subduction zone (Mw 7.2-7.3, close to the selected EGF magnitude) for which long-period Green's functions (100-2000 sec) remain very similar, even if event epicenters are separated by about 650 km. This justifies the possibility of using the 2002 foreshock as an EGF for the whole rupture process of the Sumatra earthquake and shows more generally the very broad range of application of EGF technique. Then, a specific analysis reveals that seismic moment magnitude is close to 9.1 (seismic moment equal to 5.6 x 1022 N m). Moment release analysis along the Sumatra--Andaman trench shows two main slip episodes: one next to the northern extremity of Sumatra (∼20-m slip) and the other one along the Nicobar Islands (∼10-m slip), with a global extent of 1150-1200 km. Rupture velocity varies between values around 2.5 km/sec in the first half of the rupture and values closer to 2 km/sec in the second half. Total duration imaged by Rayleigh waves is 580 sec (±20 sec) and no activity of the fault is found in the time scale between 600 and 2000 sec. In the hypothesis of even longer timescale slip, this phenomenon would be of the order of 10%-20% of the global moment and likely restricted to the Andaman Islands. [ABSTRACT FROM AUTHOR]