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Utilization of Satellite Geophysical Data as Precursors for Earthquake Monitoring
Published in Ramesh P. Singh, Darius Bartlett, Natural Hazards, 2018
Earthquake swarms are sequences of earthquakes closely clustered in space and time, in which no single earthquake dominates in size (Scholz 2002; Mogi 2003). Swarms originate in the crust from ambient stress generated by volcanic or tectonic activity (Mukhopadhayay and Dasgupta 2008). A large number of earthquakes have occurred beneath the Andaman Sea, east of the Nicobar Islands, starting 26 January 2005. The swarm activities were centred near 8° N and occurred mainly during 26–31 January 2005 following the great earthquake of 26 December 2004. GRACE gravity changes during December 2004 to January 2005 up to March 2005 show drastic changes in this region, which has been correlated with the swarm activities. Related tectonic studies over the Sumatra–Andaman arc region and the fault solutions have also indicated strong correlation at a particular depth.
Development Of Multi-Component Borehole Instrument For Earthquake Prediction Study:
Published in H. Ogasawara, T. Yanagidani, M. Ando, Seismogenic Process Monitoring, 2017
H. Ishii, T. Yamauchi, S. Matsumoto, Y. Hirata, S. Nakao
Hypocenter distributions of the swarm are shown in Figure 4 (JMA 1997). It is easily seen that the station is located very close to the earthquake swarm area. Total number of earthquakes reached to more than 9,000. Three strain and two tilt components observed by the multi-component borehole instrument are illustrated in Figure 5 from 24th February to 17th March, 1997. It is found that from 3rd of March anomalous strain and tilt variations started and became stable after about 10th of March. We can also realize strain and tilt steps corresponding to large earthquake occurrence. It is considered that anomalous variations are related to movement of material like magma or hot water near the surface in the upper part of the crust. The enlarged traces at the beginning of the swarm are presented in Figure 6. The start of the anomalous change in both tilt and strain is not so clear though the earthquake swarms started at 0:20 of 3rd of March. In order to find the beginning of the anomalous change we have to design effective method. After trials of several methods we have found a useful method to find anomalous precursory phenomena. Figure 7 shows variation of descending tilt vector from 24th of February to 10:40 3rd of March, 1997. It is seen that usually daily tidal tilt variation shows closed shape. However, before the beginning of earthquake swarm, tilt vector shows different behavior from usual and descend into direction of acting tectonic stress. Then the earthquake swarm began, and the first large earthquake happened after an acceleration in tilt. Figure 8 is the figure combined from Figure 7. It is clear that the tilt vector shifts from usual pattern from 1st of March, namely, two days before the start of earthquake swarm. We can easily predict occurrence of the earthquake swarms by looking at this kind of figure. Next, we consider strain data obtained from the multi-component borehole instrument. We computed principal strain from observed 3-component strain data. Figure 9 represents maximum principal strain from 24th of Feb. to 22:40 3rd of March, 1997 where plot of strain is shifted for every day to avoid overlap of plot and to see variation clearly. This strain shows direction and magnitude of expansion strain. It is interesting that the strain is becoming large and the direction converges to the acting tectonic stress before the beginning of the earthquake swarm on 3rd of March. Then it accelerates before large earthquake occurrence like rock mechanics experiments. Considering both tiltmeter and strainmeter results, occurrence of earthquake swarm and first large earthquake can be clearly pointed out.
Semi-automated template matching and machine-learning based analysis of the August 2020 Castelsaraceno microearthquake sequence (southern Italy)
Published in Geomatics, Natural Hazards and Risk, 2023
S. Panebianco, V. Serlenga, C. Satriano, F. Cavalcante, T. A. Stabile
In this context, an important role is played by micro-earthquake sequences, during which the seismic events are spatially, temporally and dynamically related to each other. Mogi (1963) classified three distinct types of seismic sequences: a) mainshock-aftershock; b) foreshock-mainshock-aftershock; c) earthquake swarm. Each distinct typology is characterized by a different pattern of successive shock occurrence, in turn related to the structural state and the space distribution of stress inside the crust. Over the years, seismologists dug into waveforms generated by microearthquake sequences for several purposes. The most immediate is to gain insights on the geometry of fault structures at seismogenic depth: in that way, previously unmapped fault structures as well as geometrical complexities due to the presence of multiple fault strands, kinks, stepovers have been illuminated by the space distribution of earthquake hypocenters, obtained by both absolute and relative seismic location methods (e.g. Waldhauser and Ellsworth 2002; Valoroso et al. 2013; Shelly et al. 2015; Stabile et al. 2021). The accurate study of micro-earthquake sequences may also allow gaining precious insights on the foreshock behaviors and on nucleation processes (Ross et al. 2019b), on the role of fluids and/or creep governing the migration of hypocenters along faults (e.g. Dublanchet et al. 2015; Shelly et al. 2016) and the aftershock propagation (Miller et al. 2004), the role of static stress transfer in the event-to-event triggering (Stabile et al. 2012; Ellsworth and Bulut 2018).
Taupō volcano’s restless nature revealed by 42 years of deformation surveys, 1979–2021
Published in New Zealand Journal of Geology and Geophysics, 2022
Peter M. Otway, Finnigan Illsley-Kemp, Eleanor R. H. Mestel
Three days later an earthquake swarm commenced abruptly in the Kinloch area and then appeared to migrate in a southeast direction through the centre of the lake (Grindley and Hull 1986; Otway 1986). One week after the swarm started (23 June) the Kaiapo Fault ruptured, with a downthrow of 47 mm to the northwest (towards KH), which increased to 50 mm by early September, as observed precisely by the Kaiapo tilt levelling pattern. Windy weather delayed further lake levelling observations, but five days after the fault break, KH was found to have subsided 40 mm and then stabilised briefly before resuming subsidence at a much slower rate. By January 1984, it had returned to within 2 mm of its October 1982 height. Meanwhile Rangatira (RA), on the opposite side of the fault, continued rising, peaking and virtually stabilising at 55 mm above its August 1983 height by January 1984 (Figures 4A and 5C, S1). The fault belt deformation is discussed in more detail in a later section.
Seismic Damage Prediction of Masonry Churches by a PGA-based Approach
Published in International Journal of Architectural Heritage, 2019
Gianfranco De Matteis, Mattia Zizi
Furthermore, aftershocks interested a 40 km wide area and notable extension of co-seismic displacement were recorded (Gruppo di Lavoro INGV sul terremoto in centro Italia 2016, Pucci et al. 2017). To prove the exceptionality of the earthquake swarm, it is worth noticing that the last significant seismic event has been recorded in Muccia (MC) on April 10, 2018 with a Mw of 4.6. Due to this seismic event (namely Amatrice-Norcia-Visso sequence), 140 municipalities belonging to 4 regions and 10 provinces were included in the seismic crater. Some small and ancient municipalities were completely destroyed with heavy damages occurred also on cultural heritage (churches, historical palaces, etc.). In particular, churches were affected by a huge damage, evidencing the need to increase scientific and technical knowledge aimed at improving existing methodologies for preserving such constructional types, despite their notable intrinsic seismic vulnerability (Brandonisio et al. 2013; Da Porto et al. 2012; De Matteis, Criber, and Brando 2016; Hofer et al. 2018; Sorrentino et al. 2014; Valente, Barbieri, and Biolzi 2017).