Anisotropic structure beneath central Java from local earthquake tomography

Abstract

[1] In this study we present the new tomographic code ANITA which provides 3-D anisotropic P and isotropic S velocity distribution based on P and S traveltimes from local seismicity. For the P anisotropic model, we determine four parameters for each parameterization cell. This represents an orthorhombic anisotropy with one predefined direction oriented vertically. Three of the parameters describe slowness variations along three horizontal orientations with azimuths of 0°, 60°, and 120°, and one is a perturbation along the vertical axis. The nonlinear iterative inversion procedure is similar to that used in the LOTOS code. We have implemented this algorithm for the updated data set of central Java, part of which was previously used for the isotropic inversion. It was obtained that the crustal and uppermost mantle velocity structure beneath central Java is strongly anisotropic with 7-10% of maximal difference between slow and fast velocity in different directions. In the forearc (area between southern coast and volcanoes), the structure of both isotropic and anisotropic structure is strongly heterogeneous. Variety of anisotropy orientations and highly contrasted velocity patterns can be explained by a complex block structure of the crust. Beneath volcanoes we observe faster velocities in vertical direction, which is probably an indicator for vertically oriented structures (channels, dykes). In the crust beneath the middle part of central Java, north to Merapi and Lawu volcanoes, we observe a large and very intense anomaly with a velocity decrease of up to 30% and 35% for P and S models, respectively. Inside this anomaly E-W orientation of fast velocity takes place, probably caused by regional extension stress regime. In a vertical section we observe faster horizontal velocities inside this anomaly that might be explained by layering of sediments and/or penetration of quasi-horizontal lenses with molten magma. In the mantle, trench parallel anisotropy is observed throughout the study area. Such anisotropy in the slab entrained corner flow may be due to presence of B-type olivine having predominant axis parallel to the shear direction, which appears in conditions of high water or/and melting content.

Geothermal exploration using geochemical data; study case: Parang Wedang geothermal field, Indonesia

“…Finally, we show that rather than high temperature system, the Parang Wedang geothermal system was a low to a moderate geothermal system. Our interpretation is consistent with seismology tomography studies that indicate magmatic fluid pathway from the subduction of Eurasian and Australian plates [11].…”

Multiscale Seismic Tomography Imaging of Volcanic Complexes

“…At 15 km depth beneath Toba and Helatoba volcanoes we observe anomalies which are slightly stronger than 10%. This is likely a signature of volcanic chambers and magma paths, however this value is not higher than observed in normal volcanic areas like Central Java (Koulakov et al, , 2009c and Central Chile (Koulakov et al, 2006) which will be discussed in next chapters. In the mantle the amplitude of anomalies is less than 7% that is relatively low for volcanic areas.…”

“…Three of them describe slowness variations along three horizontal orientations with azimuths of 0°, 60° and 120°, and one is a perturbation along the vertical axis. Here I discuss the results of anisotropic inversion which are presented in Koulakov et al, (2009c). The most important feature at shallow depths ( Figure 12) is a strong low-velocity anomaly beneath the middle part of Central Java which is highlighted with violet dotted line.…”

Subduction Zone Tomography

“…Long (2013) has made a detailed review of seismic anisotropy studies of subduction zones; in particular, studies using shear-wave splitting measurements and receiver functions. So far, P-wave anisotropy tomography has been applied to investigate the 3-D anisotropic structure in a number of subduction zones, including New Zealand (Eberhart-Philips and Henderson 2004; Eberhart-Philips and Reyners 2009), Northeast Japan (Ishise and Oda 2005;Wang and Zhao 2008Cheng et al 2011;Huang et al 2011a;Tian and Liu 2013), Southwest Japan (Ishise and Oda 2008;Zhao 2012, 2013), South Kuril Liu et al 2013a); Java (Koulakov et al 2009), Central America (Rabbel et al 2011), Alaska (Tian and Zhao 2012), Eastern Tibet (Wei et al 2013), North China Craton above the stagnant Pacific slab (Wang et al , 2014Tian and Zhao 2013), and western USA (Huang and Zhao 2013c).…”