We propose an extended 3D space (longitude, latitude, and depth) epidemic-type aftershock sequence (ETAS) model for seismicity forecasts beneath the greater Tokyo area (the Kanto region), which also takes into account the effects induced by the M9 Tohoku-Oki earthquake of 2011. The model is characterized by a number of 3D location-dependent parameters, such as the background seismicity rates, and the productivity rate induced by the Tohoku earthquake. These allow production of high-resolution predictive mappings in zones where hypocenters are densely populated. The optimally inverted 3D spatial images of the characterizing parameters effectively discriminate seismicity features in the crust and near the plate boundaries. The success of the model is demonstrated using short-, intermediate- and long-term probability forecasts of intermediate and large earthquake occurrences beneath the Kanto region.
In this manuscript, we first apply the temporal ETAS model to see the change of seismicity in the Kanto region, before and after the M9 Tohoku-Oki earthquake. Then, we analyze the seismic activity beneath the Kanto Plain using a 3D model taking the induced effects of the M9 Tohoku-Oki earthquake into consideration. The model characteristic parameters are location dependent and we estimate them using an empirical Bayesian method (Akaike 1980) to forecast the probabilities of occurrence beneath the Kanto plain. Also, we show the inverted 3D spatial images of such characteristic parameters illustrate the discriminative seismicity patterns in the crust and on the subducting plates boundaries.
EARTHQUAKE 3D Enhanced Edition..epubl
DOWNLOAD: https://byltly.com/2vCSEd
Fitting of temporal models. The identical rising black lines in the three panels show the cumulative numbers of earthquakes of M4 and larger in the Kanto region, against the elapsed time over the entire period. a The red cumulative curve shows the theoretical numbers of M4 earthquakes and larger, from the beginning of the period. This was estimated using the ETAS model, fitted in the target period up until the time of the M9 Tohoku-Oki earthquake (indicated by the right side vertical dotted line), and extrapolated after that. b The thick gray line represents the expected cumulative curve obtained from model Eq. (1). c This panel shows the decomposition of the expected contributions to earthquake numbers, in the combined model Eq. (1), by background, self-triggering, and induced components
Using the fixed reference parameters in Table 1, we determined the Delaunay functions for the location-dependent parameters in Eqs. (2) and (3) (see Section S2.3 for the detail). In spite of the intensive computation required, the proposed models should be robust and should work reasonably well for future earthquake prediction in the 3D cuboid beneath the entire Kanto area. This expectation is found on the generation of optimal solutions for the parameters and subsequent forecasts at all vertices of the Delaunay tessellation; that is, the colored particles in Fig. 3. Linear interpolation, within the tetrahedron formed by the four nearest particles, then generates those statistics for any location within and beneath the Kanto region.
Sectional images of the background seismicity rate μ-values. The unit of the log-scale color legend corresponds to the reference value \(\bar\mu \) in Table 1 (Reference). The superimposed black disks corresponding to their sizes represent M6 and larger earthquakes, from the JMA Hypocenter Catalog, that occurred over the last 96 years. The depth ranges used in plotting the black disks are the same as those in the Fig. 4 caption
Similarly, the background rates are high beneath the central part of Kujukuri Beach (Chiba East Coast, around 140.4E, 35.5 N). We know that earthquake swarms, associated with slow slips on the PHS, occur here (Sagiya 2004; Hirose et al. 2014). However, directly below this region, there is another intensive earthquake cluster in the PAC. There are also swarms in shallow crust in the western part of Kanto Plain, along a zone from north to south that includes the Mounts Fuji and Hakone.
The background rates are also high beneath northern Tokyo Bay on the upper interface of the PAC Plate. There have been a considerable number of historically disastrous earthquakes beneath the Tokyo Bay area (Utsu 1982, 2002). It is not known whether all these historical earthquakes, of long ago, are related to zones of high background occurrence.
We can, however, confirm, according to the JMA catalog, that many large earthquakes of M6 and larger (black disks in Fig. 5), from the last 96 years, occurred at places where background rates are high. This mapping does not include the large aftershocks of the 1923 great Kanto earthquake of M7.9.
The KM9 images in Fig. 6 characterize the sizes of induced effects in the Kanto volume resulting from static stress changes after the 11 March 2011 M9 Tohoku-Oki earthquake. The zones of very high KM9 clearly include the great majority of the earthquakes that occurred in the month after the event (white circles in Fig. 6). The remarkable exceptions include shallow statically induced major earthquakes and their aftershocks (Fig. 6a); for example, at the northwestern edge (M6.7 Northern Niigata Prefecture), and also at Fujinomiya (Eastern Shizuoka Prefecture) of M6.4. Another inducement area is seen (Fig. 6d) in the zone near the upper surface of the PHS, 50 km NE from the Lake Kasumigaura. This seismicity enhancement cannot be explained solely by the static stress changes. More detailed studies are in Kumazawa and Ogata (Kumazawa 2013).
The inducing parameter KM9 appears to be intensively high in only some parts of the PAC Plate with high μ rates offshore in the east. On the other hand, the correlation with the background seismicity rate is less clear at about 40-km depth or deeper on both plates, and we see fewer triggering effects than in the eastern offshore area. There is a zone of high KM9 values on the PHS off the east coast of the Boso Peninsula, which corresponds to the swarm zone associated with the triggered slow slip, 2 days after the M9 event (Hirose et al. 2014). On the whole, the inducing effect of KM9 is highest in the nearby part of the rupture source of the M9 Tohoku-Oki earthquake, on the upper PAC Plate boundary.
These KM9 images should be carefully compared with those showing the background seismicity rate μ in Fig. 5. As seen in Figure S9b in Additional file 1, the static stress changes decreased with the distance from the M9 slip source. The mottled pattern KM9 after de-trending such effect appears very similar to the mottled pattern of the background rate μ in each panel of Fig. 5; particularly, those on the plate boundaries of PAC and PHS in Fig. 5c, d. This means that, given a similar static stress rate, induced earthquakes are more likely to occur in zones of higher background rates.
The first date 2009.11.01 precedes the 2011 Tohoku M9 earthquake, the second date 2012.05.01 is about 1 year after the M9, and the third 2018.06.30 is 7 years later. According to Fig. 7, the seismicity rate over the entire Kanto volume at 2009.11.01 is close to the estimated background rates as seen in Fig. 5. Occurrence rates increased significantly following the Tohoku-Oki earthquake, especially along the upper interface of the subducting Pacific Plate and in the north-east offshore.
Second, earthquakes in the eastern far offshore areas near the boundary of our studied region are biased towards deeper depths and dispersed, as seen in Fig. 1a, as a result of one-sided observation from land-based sensors.
Based on the hypocenter catalog for a century of earthquake events, we obtained inversion solutions for key location-dependent parameters, including the background seismicity rates, the self-exciting (aftershock) productivity rates, and the M9-induced productivity rate. The optimally inverted 3D spatial images of such characteristic parameters illustrate the discriminative seismicity patterns in the crust and on the subducting plates boundaries.
In particular, the background rate appears quite useful for long-term forecasting of large earthquakes. The external triggering factor shows the zones where the induced effect took place. These overlap with zones of high and intense background rate on the Pacific Plate boundary, but depend on distance from the M9 source. As yet, activity levels have not reduced back to those before the mega-event.
Abstract:Geoinformatics plays an essential role during the recovery phase of a post-earthquake situation. The aim of this paper is to present the methodology followed and the results obtained by the utilization of Unmanned Aircraft Systems (UASs) 4K-video footage processing and the automation of geo-information methods targeted at both monitoring the demolition process and mapping the demolished buildings. The field campaigns took place on the traditional settlement of Vrisa (Lesvos, Greece), which was heavily damaged by a strong earthquake (Mw=6.3) on June 12th, 2017. For this purpose, a flight campaign took place on 3rd February 2019 for collecting aerial 4K video footage using an Unmanned Aircraft. The Structure from Motion (SfM) method was applied on frames which derived from the 4K video footage, for producing accurate and very detailed 3D point clouds, as well as the Digital Surface Model (DSM) of the building stock of the Vrisa traditional settlement, twenty months after the earthquake. This dataset has been compared with the corresponding one which derived from 25th July 2017, a few days after the earthquake. Two algorithms have been developed for detecting the demolished buildings of the affected area, based on the DSMs and 3D point clouds, correspondingly. The results obtained have been tested through field studies and demonstrate that this methodology is feasible and effective in building demolition detection, giving very accurate results (97%) and, in parallel, is easily applicable and suit well for rapid demolition mapping during the recovery phase of a post-earthquake scenario. The significant advantage of the proposed methodology is its ability to provide reliable results in a very low cost and time-efficient way and to serve all stakeholders and national and local organizations that are responsible for post-earthquake management.Keywords: 3D change mapping; building demolition; post-earthquake management; 4K video; UAS 2ff7e9595c
コメント