Seismic event detection in urban Singapore using a nodal array and frequency domain array detector: earthquakes, blasts and thunderquakes

Detection of seismic events at or below the noise level is enabled by the use of dense arrays of receivers and corresponding advances in data analysis methods. It is not only important to detect tectonic events, but also events from man-made, non-earthquake sources and events that originate from coupling between the solid Earth and the atmosphere. In urban environments with high ambient noise levels the effectiveness of event detection methods is unclear, particularly when deployment restrictions result in an irregular receiver array geometry. Here we deploy a dense nodal array for 1 month in the highly populated city state of Singapore. We develop a new detection method based on image processing that we call spectrogram stacking, which detects anomalous, coherent spectral energy across the array. It simultaneously detects multiple classes of signal with differing spectral content and aids event classification, so it is particularly useful for signal exploration when signal characteristics are unknown. Our approach detects more local events compared to the traditional STA/LTA and waveform similarity methods, while all methods detect similar numbers of teleseismic and regional earthquakes. Local events are principally man-made non-earthquake sources, with several events from the same location exhibiting repeating waveforms. The closest earthquake occurs in peninsular Malaysia, in an area where no earthquakes have previously been detected. We also detect ground motion over a wide frequency range from discrete thunder events which show complex coupling between acoustic and elastic wavefield propagation. We suggest that care should be taken deciphering local high-frequency tectonic events in areas prone to thunder storms.Published versio

Aftershock sequence of the 1994, Mw 6.8, Liwa earthquake (Indonesia): seismic rupture process in a volcanic arc

International audienceWe present the aftershock activity following the February 15, 1994, Mw 6.8 earthquake which was strongly felt in southern Sumatra, Indonesia, near the Great Sumatran Fault (GSF). At this place, the slip rate is supposed to be low; neverthless, three M>6 events occurred along this segment during this century. No significant instrumental microseismi-city has ever been recorded there. We use data from both the regional Indonesian network and a local seismic array operating 11 days after the mainshock during one month. Aftershocks mostly locate in a broad zone of 55x20 km 2 near two active NW-trending strike-slip segments of the GSF separated by a recent caldera, Suwoh. During the experiment, the NW segment (from Suwoh up to 15 km SE of the Ranau lake caldera, an old right-stepover pull-apart) was very active. As first suggested by the aftershock distribution and the lack of coseismic rupture at the surface, the 20 focal mechanisms determined provide evidence for various post-seismic stress adjustments on secondary faults located in the Ranau-Suwoh paleo-pull-apart graben. Less than 20% of the aftershocks are directly linked to the main rupture, a nearly pure right-lateral strike-slip faulting reaching 25 km depth. A narrow seismic gap underlines the active volcanic area of Suwoh. We conclude that the rupture process along the GSF is controlled both by volcanism and structures, and that the volcanic activity affects the mechanical properties of the crust only in a narrow zone

STRUKTUR LAPISAN BUMI DI BAWAH G. TANGKUBAN PARAHU BERDASARKAN STUDI SEISMIK STASIUN TUNGGAL

Stasiun seismograf tunggal pita lebar (broadband) di G. Tangkubanparahu telah merekam sejumlah gempa jarak jauh. Gelombang gempa yang terekam telah di analisa dengan menggunakan pendekatan fungsi penerima untuk mempelajari struktur bawah permukaan di bawah stasiun. Hasil awal, berdasarkan metode pemodelan kedepan (forward) dan inversi fungsi penerima menunjukkan ketebalan kerak di bawah Tangkubanparahu adalah sekitar 30-35 km. Juga ada kemungkinan adanya dua zona kecepatan rendah di bawah G. Tangkubanparahu yang boleh jadi merupakan dua kantung magma pada kedalaman sekitar 5 km dan 25 km

The velocity structure of the volcanic plumbing system of Gede Volcano, West Java, Indonesia

We estimated the velocity structure beneath four three-component broad-band seismic stations and three short period stations in the Gede Volcano region, West Java, Indonesia by the receiver function (RF) technique jointly with H/V (Horizontal/Vertical) amplitude ratio of Rayleigh waves to constrain the 1D velocity structure around each station, and in the back-azimuth of the source considered, ultimately providing a 3D understanding of the velocity structure of the volcanic plumbing system. The stations are part of the collaborative seismological network between Center for Volcanology and Geological Hazard Mitigation (CVGHM) and Earth Observatory of Singapore (EOS). Our preliminary result suggest the depth of the Moho is about 30 km. Based on the back azimuth of the earthquakes, the receiver functions inversion and H/V amplitude radio from the earthquakes coming from the NE-SE direction exhibit strong negative signals between direct P and Pms phase correspond to a low velocity layer in the crust, predominating all broadband station stations. This is consistent with the result of previous study of travel time tomography. We observed very few earthquakes from SW-NW direction where the receiver functions show differently from the first group due to the waves travel to magmatic body. Combining results from this study and the tomography we aim is to further find the magmatic body under the volcano at shallow as well as deeper depths. Since we have 10-year data, we will be able to see the yearly evolution or changes of the magmatic system under the volcano

Magma-sponge hypothesis and stratovolcanoes : case for a compressible reservoir and quasi-steady deep influx at Soufrière hills volcano, Montserrat

We use well-documented time histories of episodic GPS surface deformation and efflux of compressible magma to resolve apparent magma budget anomalies at Soufrière Hills volcano (SHV) on Montserrat, WI. We focus on data from 2003 to 2007, for an inflation succeeded by an episode of eruption-plus-deflation. We examine Mogi-type and vertical prolate ellipsoidal chamber geometries to accommodate both mineralogical constraints indicating a relatively shallow pre-eruption storage, and geodetic constraints inferring a deeper mean-pressure source. An exsolved phase involving several gas species greatly increases andesite magma compressibility to depths >10 km (i.e., for water content >4 wt%, crystallinity ∼40%), and this property supports the concept that much of the magma transferred into or out of the crustal reservoir could be accommodated by compression or decompression of stored reservoir magma (i.e., the “magma-sponge”). Our results suggest quasi-steady deep, mainly mafic magma influx of the order of 2 m3s−1, and we conclude that magma released in eruptive episodes is approximately balanced by cumulative deep influx during the eruptive episode and the preceding inflation. Our magma-sponge model predicts that between 2003 and 2007 there was no evident depletion of magma reservoir volume at SHV, which comprises tens of km3 with radial dimensions of order ∼1–2 km, in turn implying a long-lived eruption.Published versio

PERANCANGAN BAHAN PELATIHAN BERBASIS WEBSITE DI KEJURUAN TEKNOLOGI INFORMASI DAN KOMUNIKASI BALAI BESAR PENGEMBANGAN LATIHAN KERJA BEKASI

 AbstractBalai Besar Pengembangan Latihan Kerja (BBPLK) Bekasi is a training place for government-owned skills or expertise under the auspices of the Ministry of Manpower headed by Echelon II government officials. In the Center for Job Training Development (BBPLK) Bekasi, there are various kinds of vocational training, one of which is the Information and Communication Technology Vocational School. In the Information and Communication Technology (ICT) Vocational School there are 5 (five) training programs, namely: Graphic Design, Motion Graphic Artist, Network Professional, Mobile Programming and IT Software For Business Solution. In this vocational school, they still use the manual method in processing data on training materials stored in the warehouse. The method used is by filling out the training material expenditure form, then the form is stored in their respective archive folders. This system has been running well but still has weaknesses, including if the admin is asked to find training material data quickly, the admin will have difficulty finding one by one archive that has been stored and takes a long time and taking training materials that are not in accordance with the training program and possibly there is a missing file. The research method uses data collection by means of observation, interviews and literature study. So with the design of a website-based training material inventory information system, it can make it easier to find data on the availability of training materials according to the training program and make the work process of checking training materials more effective and efficient. Keywords : training materials, system, information, inventory, website.