Holocene land level and relative sea level are affected by a multitude of processes along the west coast of Luzon Island in the Philippines. Melting of higher-latitude continental ice sheets from Last Glacial Maximum through the mid-Holocene led to eustatic sea-level rise, and the redistribution of ice and meltwater loads resulted in glacial isostatic adjustment (GIA) processes that are ongoing today even in low latitudes. Off the west coast of Luzon, the South China Sea plate subducts under the Philippine Mobile Belt at the Manila Trench, inducing elastic deformation over the megathrust seismic cycle that has a maximum amplitude somewhere between the coastline and the trench but which may still be appreciable onshore. Yet some relative plate motion is taken up onshore, as evidenced by uplifted inferred Pleistocene terraces tens of meters above present mean sea level. We have dated, slabbed, and analyzed a set of Holocene coral microatolls at the Pagsanahan site in Badoc municipality, Ilocos Norte province, on Luzon. Coral microatolls precisely track relative sea level (RSL), allowing the reconstruction of both the position of RSL and rates of RSL change. Preliminary analysis reveals the complicated interplay of multiple drivers of RSL: RSL rose rapidly until ~7400 cal yr BP, before dropping abruptly by ~1m. We surmise these reconstructions capture rapid RSL rise toward a regional mid-Holocene highstand due to meltwater input and GIA, interrupted by ~1m of coseismic uplift locally. We are working to elucidate details and identify potential causative faults.

The Bayan Har Block is a typical one of those active blocks extruded laterally from the Tibet Plateau in the Cenozoic. Also, the block has been suggested as one of the areas with frequent strong earthquakes occurring in China mainland. To date, studies on active tectonics of the block have been mainly focused on its boundary faults. Except for several boundary faults, however, some large strike-slip faults developed within the block, which appears to have divided the block into several sub-blocks. Did the Bayan Har Block accommodate its deformation mainly on the boundary faults and have a tectonically relatively stable interior? Or, was there still significant tectonic activity inside this block? The Dari fault is one of the left-lateral strike-slip faults that located in the middle region of the block. The fault is a late Quaternary active fault and the 1947 M7¾ Dari earthquake was produced by its middle and southern segment. Based on interpretation of high-resolution images and field investigations, we found that a series of linear tectonic landforms, such as fault trough valley, fault scarps, fault springs and gully offsets, etc. were formed along the Dari fault. We also suggest that the surface rupture related to the Dari earthquake is about 70 km long and the co-seismic offset was about 2-4 m determined by a series of offset gullies. Furthermore, we indentified four seismic event by trench excavations, which are dated at 13595-10657 BC、10547-7731BC、4734-3067BC、1947 AD. The recurrence intervals of these events are approximately 3000, 5200 and 5800 years. Obviously, the Dari fault can be characterized by strong late Quaternary. The fault may play an important role in the kinematics and tectonic deformation mechanism of the Bayan Har Block. Support by Science for Earthquake Resllience of China Earthquake Administration (XH192305). 

The repetitive narrative that, “Tsunami waves and receded coastal water initiated by an earthquake are closely related,” is analyzed through the sequential events that followed the earthquake, a mechanism is suggested to explain the generation of Tsunami wave deep beneath the ocean floor, where earthquake occurred under the seabed’s or in coastline; the mechanism explained how the water below build up to encompass the tremendous force that lifted the ocean water endowing it with such destructive power; it also explained characteristics related to Tsunami wave, including relation with earthquake and volcano, receding costal water, the nature of the great force of Tsunami, initial idea to calculate the magnitude of Tsunami force, the repetition of its wave; these and related issues are stated; the idea is derived based on relationship between the Magnetic Dipole Moments of the Sun & the Earth and the related energization process carried in their outer cores in addition to an important characteristics detected on earth’s surface and ocean floor, these with relevant mechanism, all based on logical analyses and deep thinking to attained the Tsunami Mechanism in response to 2004 and 2011 human tragedies; thus understanding this mechanism will help laying measures to counter the phenomenon, which will reflect positively in saving lives and mitigate its destructive force and reduce consequences of its impact on local societies and above all to understand its true mechanism.

In Japan, regional 3D stress filed by Terakawa and Matsu’ura (2010; TM2010) with the Wallace-Bott hypothesis, the direction of fault slip is parallel to the resolved stress vector on a preexisting fault, is used to estimate fault slip angles for mapped submarine faults. Then, the strong ground motions and tsunamis were simulated by using the estimated fault slip angles. However, the above method has not been adequately validated and here, we validated the above method for two focal mechanism catalogs. We evaluated the misfit angles between the rake angles from focal mechanisms and those estimated from 3D tectonic stress field with the Wallace-Bott hypothesis by fixing the fault strike and dip angles. See Ishibe et al. (2021; this meeting) for the validation results for the major active fault zones in Japan where the slip-directions are geomorphologically estimated and long-term evaluations are conducted. As a result, misfit angles are mostly small (<30 deg.) except for the source and surrounding regions of large earthquakes and swarm-like activities activated after the 2011 Tohoku-oki earthquake. Among 25 earthquakes with M6 or larger, which occurred during the pre-Tohoku period, misfit angles are <10 degrees for 20 (80 %) earthquakes and <20 degrees for 23 (92 %) earthquakes. The only two earthquakes exhibit >30 degrees misfit angles. Our results imply the validity and effectiveness of estimating fault slip angles for a specific fault with known fault geometry from the above data and hypothesis, while it requires attention to apply the method for the regions with seismically inactive and/or nearby the recent large earthquakes where the stress field have been perturbed. Acknowledgments: This study has been supported by the Headquarters for Earthquake Research Promotion of the Ministry of Education, Culture, Sports, Science, and Technology of Japan.

In Japan, regional 3D stress filed by Terakawa and Matsu’ura (2010) with the Wallace-Bott hypothesis, the direction of fault slip is parallel to the resolved stress vector on a preexisting fault, is used to estimate fault slip angles for mapped submarine faults. Then, the strong ground motions and tsunamis were simulated by using the estimated fault slip angles. However, the above method has not been adequately validated and thus, as the first attempt for such verification, we validated the above method for two focal mechanism catalogs (Ishibe et al., this meeting). Here, we validated the above method for >100 major active fault zones in Japan that the fault types were evaluated from geomorphological data. We compared fault types according to fault slip angles estimated from the 3D stress field with the Wallace-Bott hypothesis, with geomorphologically-estimated fault types. As a result, fault types obtained from the above method well coincide with those from geomorphological data for most of the major fault zones, and well reproduce the regional characteristics of fault types in Japan, while those are inconsistent for several fault zones such as several segments of the Median Tectonic Line. Our results imply the validity and effectiveness of estimating fault slip angles for a specific fault with known fault geometry from the above method and data. Furthermore, the results also suggest that the 3D regional stress field estimated from geophysical data for a limited period (~10 years) can be used as a proxy of the longer-term stress field. Acknowledgments: This study has been supported by the Headquarters for Earthquake Research Promotion of the Ministry of Education, Culture, Sports, Science, and Technology of Japan.

We have investigated shear wave splitting using seismograms from 23 broadband stations of BMKG along Central and East Java, Indonesia, recorded from January 2009 to September 2017 with the clear onset of local S phases and constrained it to the criteria of crustal anisotropy study, i.e. event depths less than 30 km with radius 100 km from each recorded station. We compared our results with the regional strain rate derived from GPS observations in Java, then divided the analysis into three regions, i.e. (1) Southern part of Java, (2) Northern part of Java, and (3) Easternmost Java and Bali region. In general, stress-induced anisotropy caused by aligned cracks associated with deformation in the overriding Eurasian plate is suggested as the cause of anisotropy in the southern part of Java and easternmost of Java since they indicate the parallel average fast direction to the direction of principal strain. Meanwhile, in the northern part of Java is more likely structural induced anisotropy from the activity of the Kendeng fault.

Eastern Indonesia is a complex tectonic configuration surrounded by four major tectonic plates: the Australian Plate in the southern, Pacific Plate in the northeastern, Philippine Sea Plate in the northern and the Sunda Block in the western. Correspondingly, this region had undergone some significant seismic activities as well as the tectonic deformation. We analyzed data from over 100 GPS stasions to evaluate the regional deformation of Eastern Indonesia. We derived the velocity field into two-dimentional strain rate tensors and then mapped the second invariant and maximum shear strain rate. Here, our strain analysis results represent the long-term tectonic deformation in some regions of Eastern Indonesia. The spatial pattern of strain rate map obtained from this research then provides an insight of the present-day tectonic condition in Eastern Indonesia and then can be used to improve our ability to assess earthquake potential of this area.

The Sumatran Fault Zone (SFZ) is one of the largest strike-slip faults in the world and it has 19 main segments which have the possibility to generate a strong earthquake in every single segment. We analyze Aceh Segment on Northern Sumatra region as one of the segments on SFZ that had generated small to moderate earthquakes (during 2009-2017) based on regional broadband seismograms data by Meteorological, Climatological, and Geophysical Agency of Indonesia (MCGA). Most of these earthquakes are inaccessible to direct observation, therefore it is not easy to determine the source parameters, such as moment seismic, stress drop, and source dimension by using field observation. The main aim of this study is to investigate the relation of source parameters from small to moderate earthquakes by using the P or S wave spectrum. The determination of source parameters from small and moderate earthquakes is important for understanding the physics of earthquakes and it can be useful for seismic hazard assessment in the study area.

In 2012, the Mw 6.8 Thabeikkyin earthquake devastated residential and public structures in Myanmar. The earthquake killed 26 people, and left 12 missing and 231 injured in the epicentral region. In addition, 201 houses, 25 schools, 13 hospitals, 35 monasteries, and 45 pagodas totally collapsed or were partially damaged. The USGS’s instrumental epicenter was near the Kyauktan fault, a western splay of the major Sagaing fault, with a shallow focal depth of ~9.8 km. Our post-earthquake field survey documented a ~45 km long surface rupture with a ~1.02 m maximum dextral offset on the main fault, between Singu town in the south, passing through Thabeikkyin town, and terminating in Sabenago village in the north. The present study clarifies the macroseismic felt intensity of the Thabeikkyin earthquake in the EMS-98 scale, emphasizing the damage pattern and macroseimic effects in Myanmar and surrounding regions, based on press reports, digital news, and post-earthquake field survey data. In the epicentral region, the macroseismic intensity reached EMS 7-8, corresponding to grade 3 to grade 4 damage along the surface rupture. Light to moderate damage, corresponding to EMS 5-6 was distributed between the latitudes of Tagaung and Myittha towns in central Myanmar. Ground shaking during the Thabeikkyin earthquake was also reported from Yangon and Bhamo cities in Myanmar and light shaking was widely felt in the Assam region of India, in Kunming in western China, and in Chiang Mai and Bangkok in Thailand. High macroseismic intensities extend further in the NE-SW direction than the NW-SE direction. Our study suggests that the peak distribution of felt intensity corresponds to the dilation fields of the USGS mainshock focal mechanism, with southward rupture directivity that caused light damage corresponding EMS-5 in Mandalay-Myittha area, >100 km from the epicenter.

Merapi volcano on the central Java is the most active volcano in the Indonesia. The vulnerability to volcanic hazards is high because Merapi is located in an area of high population density on the central Java. The satellite remote sensing method and open access satellite dataset archives are prone to be beneficial for Merapi’s hazard mapping and monitoring tasks. Here, we perform trends and cyclic activity analysis by fitting the surface temperature time series from satellite thermal infrared imagery at Merapi volcano. Both Landsat thermal imagery (with 30-meter spatial resolution) and MODIS (Moderate Resolution Imaging Spectroradiometer) temperature products (with 1-kilometer spatial resolution) are used for the analysis. The Seasonal Trend Decomposition using Loess (STL) is applied as the decomposition tool to divide up MODIS time series into different components. The trend of STL decomposition on MODIS time series indicates a subtle rising tendency. For a detailed delineation of thermal features in Merpai, the 30-meter spatial resolution Landsat thermal imagery derived brightness temperature (BT) distribution at Merapi volcno before and after eruptions in the period of 1988 to 2020 are illustrated. Plus, to investigate the temporal temperature variations, the average BT time series in Merapi crater are extracted from Landsat images and the results show a significant increasing trend of Merapi crater temperature. By contrast, change detections (pixel-over-pixel comparison) of average BT distribution from 1988 to 2020 are conducted to inspect the spatial temperature variations in Merapi volcano. In this study, satellite remote sensing approach provides insights in thermal features at a larger spatial and temporal scales on this renowned active volcano in the past three decades, which is generally not available for the on-site measurements. This study provides the valuable surface thermal information for exploring the subsurface volcanic structures.

Himalayan Orogen, which is located in the place of the continent-continent collision between the Indian and Eurasian plates since 50Ma ago, has a very complex deep and shallow tectonic pattern. Here we reconstruct the main features of the deep structure from surface wave tomography and receive functions in order to understand the modality of the convergence and collision. We collected seismic data from CENC, IRIS and Nepal experimental. Based on the seismic data, using surface wave tomography, we calculated the group velocity at the periods from 8s to 100s and applied simulated annealing algorithm to simultaneously inverse the velocities and thicknesses and identified the Moho depth and the bottom of lithosphere. Moreover, we imaged the Moho structure beneath Himalayan orogeny and its adjacent areas with RF analysis. The Himalayan block (HM) is covered by a high velocity anomaly of about 5% indicating a relatively thin asthenosphere with high velocity. The Vs models demonstrate the leading edge of the subducting Indian slab reaches up to Bangong-Nujiang suture belt (BNS). It indicated that the crust with the thickness of about 65 km in HM and the lithosphere ( ~160 km) from the velocity values and their offsets. The earthquakes are collected which occurred in the vicinity of the study area with magnitudes greater than or equal to 3.0 since 1930. The epicenters in Himalayan orogen is relatively deeper than that northern BNS, more deep focus earthquakes are located in the uppermost mantle. Along some sections in the south of BNS, the focal depth is relatively deep. Especially in the Himalayan block (HM), south of the YZS, more deep-source earthquakes (depth greater than 70 km) occurred in the crust and upper mantle lid. The study is supported by the Chinese National Science Foundation (41774069) and National Key Program (2017YFC1500304). 

This study introduces an improved hypocentral version of the space-time Epidemic-Type Aftershock Sequence (ETAS) model, entitled as the 3D finite source (3D-FS) ETAS model, and applies it to the analysis of the Southern California earthquake catalog. By stochastic reconstruction, we are able to reconstruct the patterns of aftershock productivity density along the mainshock ruptures. Detailed analysis of the productivity patterns reveals that: (1) Directly triggered aftershocks make up 21 to 41 percent of all earthquakes within the mainshock rupture areas, and show significant spatial heterogeneity and temporal migrations; (2) Major aftershocks tend to locate in low productivity areas, at the edges of clusters formed by small aftershocks; (3) Large slip areas are depleted of aftershocks, over 60 percent of all productivity distributes in areas with slip less than 0.3 times of the maximum slip, and the trajectory of the productivity pattern on the fault plane demonstrates apparent compensation to coseismic slip. We relate the difference in triggering abilities of four mainshocks to the heat flow in corresponding regions. Simulation results suggest that the 3D-FS ETAS model has apparent advantages of improving the performance of short-term aftershock forecast. Moreover, the later aftershocks are more correlated with the locations of subsequent events than earlier aftershocks, suggesting that the migration of aftershocks is important for mitigating aftershock hazard.

Xinjiang is located in the central part of the Eurasian continent. To the north are the Siberian block and the Mongolia arc tectonic belt formed by the southern compression of the block. To the south is the Qinghai-Tibet plateau formed by the collision of the Eurasian Plate and the Indian plate. Tianshan Mountains are one of the most active fault zones, and large earthquakes are mainly distributed in this area. The dynamic mechanism between the active characteristics of the main fault zones in the Tianshan orogen and the seismogenic stress field has not been clearly understood. Thus our research calculated key factors such as crustal deformation, stress/strain accumulation rate, elastic strain energy density and coulomb stress change rate by a finite element numerical model with GPS and other actual observation data as constraints. The results show that the velocity field is basically consistent with the actual GPS observations in the study area, except for slight differences in the Pamir area near the model boundary. Furthermore, the distribution of elastic strain energy density in major fault zones is primarily consistent with the actual seismicity, verifying the reliability of the numerical model and the results. Combined with the latest observation results and numerical simulation results, it is found that the fault and seismicity in the study area are mainly controlled by the principal compressive stress in the proximal north-south direction, which in line with the main observation characteristics. At the same time, the northern boundary of the Pamir Plateau - Tashkurgan Fault (TKF), the eastern boundary of the Tianshan orogen - Maidan Fault (MDF) and Xingdi Fault (XDF) are highly likely to have large earthquakes in the future, which should be paid close attention to. 

The southeastern Tibetan Plateau (SETP) is well known for its large strike-slip faults, their high slip-rates and the high potential of seismic hazards. However, little has been known about the vertical uplift of the region, despite the fact that thrust faults with low slip rate still be able to nuclide devastating earthquakes, with one of the best examples of the 2008 M 8.0 Wenchuan earthquake. One of the biggest challenges in quantifying the tectonic uplift is due to the geomorphic markers of vertical seismic offsets are quickly smoothened by erosion in the tropical or sub-tropical regions, which is difficult for geologists to quantify the tectonic uplift using traditional geological methods. Another important factor lies in the nature of the active folds and blind thrusts, both contributing to the vertical tectonic uplift, but difficult to be identified and investigated. Here, we use geomorphic analysis combined with geodetic data to better investigate the recent tectonic uplift in the SETP on a regional scale. We quantify the differential uplift in the SETP recorded in the long-term landscape evolution and with geomorphic indices and compare them with decadal leveling data and millennial scale fluvial terrace data. The results show that the northwest of the SETP underwent higher uplift rates compared to its southeast areas, which is in agreement with the GPS and the leveling results. Essentially, the geomorphic indices build two value ranges that are spatially clustered and separated by the transverse thrust fault system, that are oblique/perpendicular to the major strike-slip faults. The geomorphic indices indicating rapid uplift rates spatially correspond with high rates derived from leveling data on the hanging wall of the Muli thrust fault. The results suggest that the transverse thrust faults play a significant role in building up the topography.  

The Sichuan-Yunnan region is located in the southeastern edge of the Qinghai-Tibet Plateau, and its tectonic activity is not only controlled by the collision of the Indian plate and the Eurasian plate, but also by the blocking of the hard Yangtze Basin. As a result, the region behaves as lots of fault system and earthquakes occurred frequently. In this study, we comprehensively use geological structure, seismic geology, and deep inversion results to establish a two-dimensional elastic finite element model of Sichuan-Yunnan region for preliminary attempts of earthquake prediction. It’s necessary to know the regional initial tectonic stress for the numerical analysis of the medium-and long-term seismic hazard. Firstly, we established a 2-D finite element model with the regional geological structure data and the GPS observation data as the constraint condition, considering the drag force of the regionally flexible lower crust to the brittle upper crust, and obtained the regional stress growth rate. Then, we estimated a possible initial tectonic stress of the region, based on the Coulomb-Mohr rupture criterion and the regional historical strong earthquake information. Next, we orderly reproduced the historical strong earthquakes occurred in this region, by using the calculated tectonic loading stress rate and stress disturbance value caused by the historical strong earthquakes. However, the initial stress field obtained by the deduction is only a possible value, not the true value. Therefore, we generated a large number of independent random different possible initial values within the reasonable range by using the Monte Carlo random method, which all can ensure the historical strong earthquakes orderly occur, and the stress evolution will be different in the future. Finally, we got the probability distribution map of possible future seismic risk in the region through statistical analysis. 

Since the late Cenozoic, the northeastern margin of the Tibetan Plateau has experienced strong tectonic activity and frequent large-scale earthquake activities, and developed a series of large-scale strike-slip faults and thrust faults. So far, we have no clear understanding of the distribution of tectonic stress field, strain distribution and seismogenic mechanics in the main fault zones of the area. In this paper, a three-dimensional viscoelastic finite element numerical model for the northeastern margin of Tibetan Plateau is established. The model is 1400 km long from east to west, 800 km long from north to south, 100 km deep and covers 27 major faults. Using the CRUST1.0 elastic model and considering the difference of viscosity structure, we calculated the surface deformation, three-dimensional tectonic stress field and strain field in this area with the actual GPS observation data as the model boundary conditions. The results show that the simulated surface velocity field is basically consistent with the actual GPS observation data in the study area. The high value areas of horizontal maximum shear stress, horizontal maximum shear strain and maximum shear strain rate are banded, and they are concentrated near the main fault zone and basically consistent with the strike of the fault zone. The stress accumulation of Altyn Tagh fault zone, west segment of East Kunlun fault zone and middle segment to east segment of Haiyuan fault zone is large, which is conducive to the preparation of large earthquakes, which is more consistent with the distribution of historical large earthquakes, and can also explain the dynamic origin of the 1920 Haiyuan M8.5 earthquake. This study is helpful to understand the present tectonic stress field and the activity of main fault zones in the northeastern margin of the Tibetan Plateau 

Abstract: Analysis of fluvial landform response to the tectonic activities and climatic fluctuation is largely based on the assumption that stream networks are relatively static. However, recent researches has proven that the divide can migrate over time and the mobility of stream network can be quantitatively depicted by a series of geomorphologic metrics across divide. Previous geometry and kinematic and physical-simulation researches in active orogenic belt have suggested the stream longitudinal profile and footwall relief are sensitive to spatial-temporal patterns of the normal fault evolution. Based on the results of landscape evolution numerical simulations that are different in tectonic conditions, we use the divide asymmetry index (DAI) to evaluate the mobility of drainage divide and conclude the migration characteristics. We suggest the divide tend to migrate to the side with high uplift rate and the migration process commonly lags the tectonic activities and has great difference in response to the various tectonic evolution progress of active normal fault. We applied the model to LangShan piedmont fault (LSPF), whose segmentation has been proven by geomorphic and kinematic studies, the result of divide mobility demonstrates the uplift of LangShan is govern by the LSPF, while the LSPF has experienced complicate extending, tilting and linkage process.