Northeast China and its adjacent areas located in the central East Asian continent, are of great significance to explore the tectonics and evolution of the eastern segment of the Central Asian Orogenic Belt (CAOB). The eastern segment of the CAOB has traditionally been subdivided into a series of blocks, in which the Xing'an Block including the Great Xing’an Ranges is a fault-surrounded block, which is located along the southeastern margin of the CAOB. However, the mode of convergence and amalgamation as well as the process of tectonics and evolution of the Xing’an Block and adjacent Erguna Block and Songliao blocks are still in controversy.The data of large dynamite shots from the deep seismic reflection profile can effectively track the lower crust, Moho, and upper mantle structure on the profile. In this paper, 26 dynamite shots and 4 middle shots are used to reveal the deep structure beneath the Great Xing’an Ranges and adjacent areas.The near west-east single-coverage dynamite shots’ profile shows that beneath the Xing’an Block, dense lower crust and relatively flat Moho structure which is located at around TWT 12s (about 36 kilometers thick) are obtained, which are considered to be related to the post-orogenic extension of the crust. At the upper mantle, an eastward-dip reflection fabric, and a westward-dip reflection fabric can be tracked on the western and eastern part of the profile respective, which are supposed to be the relics of the convergence and amalgamation between the blocks. According to these pieces of evidence, Erguna Block may suture eastward Xing’an Block, besides, Songliao Block may subduct westward Xing’an Block. A reflection interface at about TWT 20s (about 80 kilometers thick) is also tracked on this profile, which is speculated to be the bottom boundary of the lithosphere.

As the northern margin of NE Tibetan Plateau, which is a natural laboratory to understand the mechanism of the lateral growth of the Tibetan Plateau and its interaction with the Asian continent, the Qilian orogen still has active tectonic activities. Here we present a high resolution receiver function image along a 400-km long dense broadband seismic profile traversing the entire Nw Qilian orogen. Based on our observations, a significant Moho step across Northern Qilian Fault has been detected, suggesting that the Alashan Block crust has not underthrust southward beneath the Qilian orogen. The interface which deepens from north to south lies at the bottom of the upper crust of the Qilian orogen, may playing an important role in topographic uplift and crustal thickening at NE Tibetan Plateau. Furthmore, two strongly deformed interfaces at Moho depth beneath Northern Qaidam Fault shows strong convergence between the Qilian orogen and QaidamBasin in the middle-lower crust. Thus, we prefer an entire crust thickening mechanism with an intracrustal decollement at the bottom of the upper crust.

    Based on the focal mechanism solutions of 2600 M_L≥3.0 earthquakes in Sichuan and Yunnan area from January 2000 to March 2017, the focal mechanism quantitative classification and stress field inversion are carried out for the sub blocks and fault zones with relatively dense focal mechanisms. Using the focal mechanism solutions of 727 M_L≥4.0 earthquakes from January 1970 to March 2017, the regional stress tensor damping method is used to inverse the spatial distribution of principal compressive stress in Sichuan and Yunnan area before and after Wenchuan Ms8.0 and Lushan Ms7.0 earthquakes, and the temporal and spatial evolution characteristics of current stress field are discussed.    The focal mechanism is mainly strike slip type in Sichuan and Yunnan area, but there are local differences. The Longmenshan fault zone is dominated by thrust type earthquakes, while the Mabian-Yanjin fault zone has relatively more strike slip and thrust type earthquakes, the types of earthquakes in Sichuan Basin are complex, and there is no obvious dominant type. The stress field in Sichuan and Yunnan area has obvious subarea characteristics, and it rotates clockwise from north to south. The principal compressive stress direction in Sichuan experiences EW-NW-EW rotation from west to East. The principal compressive stress direction in Yunnan is NNE in the west, NNW in the East, forming an inverted "V" shape in space. Before and after the Wenchuan M_S8.0 and Lushan M_S7.0 strong earthquakes, the stress field in the Longmenshan fault zone changed greatly, followed by the Sichuan Basin and its surrounding areas, and there was no obvious change in other areas of Sichuan and Yunnan.

The Tibetan Plateau is formed by the India–Asia collision which has received extensive attention from the academic community due to its special dynamic background and unique topographic features. The collision between two plates has also caused the extrusion of the northeastern margin of the Tibetan Plateau. Since the Late Cenozoic, intense compression and uplift have occurred continuously. This area is still in an active stage of lithospheric deformation and is a critical area for the study of the orogenic process. In this study, we use the waveform gradiometry(WG) method to process three-component data recorded at 676 seismic broadband stations by dense temporary seismic network(ChinArrayΠ) from October 2, 2013 to December 31, 2014. We calculate the fastest propagation direction of seismic waves through the waveform gradient method. The surface waves of the radial and tangential components of each sub-network can be obtained by coordinate transformation of the original data. Using the joint weighted inversion and reducing velocity method, the spatial gradient is obtained. Analyze the spatial gradient in the time domain to deduce the corresponding phase velocity and other seismic parameters. Based on the results of our tomography, the subsurface structure of the northeast margin can be further studied. The geodynamic process of the northeastern Tibetan plateau can be further analyzed based on the high resolution velocity and anisotropy.

The earthquake potential hazard around the off coast of the West Sumatra-Bengkulu is investigated based on the availability of pre-seismic surface displacement data and the shallow crustal earthquake catalog data of the year 1907-2016. Using our previous study result of local covariance functions and the correlation dimension (Dc) relationship with the b-value are used to estimate maximum horizontal crustal strain rate (Shmax) and Dc around the study area. The Shmax is estimated based on the horizontal displacement data using least square prediction by employing local covariance functions. The Dc is estimated based on the b-value using the maximum likelihood method with a constant number by assuming that the regional b-value is equal to 1. Furthermore, using the spatial correlation of Shmax and Dc, it can be characterized the possibility of earthquake potential hazards existence around Batu-Siberut Island. The hypothetical source model is defined by referring to the dip and width fault parameter of the 1935 event. Based on the source model, the peak ground acceleration (PGA) is estimated using the Ground Motion Prediction Equation (GMPE) referred to in our previous study. The result shows that the level PGA around 0.5 to 0.7g could reach around Batu-Siberut Island at the base rock. To better understand the potential ground shaking, the evaluation of PGA at the surface is then estimated by including the amplification factor. The amplification factor is calculated using the Horizontal-Vertical Spectral Ratio (HVSR) method of the BMKG data around Pulau Batu and Mentawai station. The PGA estimated at the surface is around 0.7 to 1.47g, reaching the possible maximum MMI scale. The results obtained in this study might be very beneficial for earthquake mitigation and modeling efforts for the possible potential of the earthquake hazard study and future analysis.

Semarang is one of big city and dense of population numbers in Central Java, Indonesia. This region has vulnerability of seismic hazard due to existence of active fault. These faults are Semarang fault, Ungaran fault and Rawapening fault. Map of seismic microzonation is needed for considerations and planning of Detail Engineering Design (DED) of buildings or infrastructure that are earthquake resistant. The use of this map is expected to reduce the impact of risks that may be posed. In mid-2019, we deployed seismic instrument at 141 points scattered in the area with a distance each point about 2 to 3 km. The experiment aims to estimate shear wave velocity (Vs30) in the Semarang region. The Vs30 is one of parameters that used to identify the seismic hazard potential. We used the Multichannel Analysis of Surface Waves (MASW) method using 24 geophones of the vertical component with the frequency of 4.5 Hz. The values provide information of site classification at surface down to 30 meters depths. The preliminary results reveal that Vs30 value in range of 189.58 - 365.64 m/s for medium soils (SD). This medium soil type (SD) almost dominates all areas except in the northern part of Semarang City. The northern part is dominated by soft soil (SE) with Vs30 values ​​in range of 102.4 - 173.39 m/s. We interpret that the areas with medium soils type has low relatively potential of seismic hazard due to the seismic wave attenuation. 

Within Southeast Asia the focus of earthquake hazard studies has been primarily on regions associated with major fault systems, which serve as bounding structures for crustal blocks, and can host extremely damaging earthquakes.  However, over the past few decades there have also been moderate earthquakes (Mw 5 – 6+) within, and adjacent to Thailand that have been damaging in spite of their more modest size. These earthquakes occur on poorly understood fault systems, and anticipating their occurrence is particularly difficult. There are at least 16 known active faults throughout Thailand, most of which could be capable of generating Mw 6+ earthquakes. Here we analyze the settings and effects from three recent, damaging, moderate-sized earthquakes in northern Thailand, that are examples of this, often hidden, seismic hazard. These include the 2006 M5.1 earthquake occurring near the city of Chiang Mai, the 2014 M6.3 earthquake occurring near the city of Chiang Rai, and the 2019 M6.4 earthquake occurring near Thai-Laos border (magnitudes are those reported by TMD). The Chang Mai earthquake, although relatively small, occurred in a suburb of Chiang Mai city and caused moderate damage in the affected area. The Chiang Rai earthquake is the largest instrumentally recorded earthquake in Thailand and also the most damaging in Thailand; producing more than $300 million in damages, and damaging 9000 buildings including 73 schools (destroying 5 schools). The Thai-Laos border earthquake caused significant damage to the Thai communities along the Thai-Laos border in Nan province. Each of these events was extremely disruptive and damaging, and points out the earthquake hazard in regions bounded by major active tectonic structures, that affect the overall stress conditions. Although these active faults are not deforming at high rates, their earthquake potential and broad distribution throughout northern Thailand make them an important hazard to be considered.

Recent devastating events such as the 2012 M_W 6.7 Negros Oriental and 2013 M_W 7.2 Bohol earthquakes have brought attention to seismic hazards in the central Philippines. Situated between Negros and Bohol, Cebu Island is cut by the Central Cebu Fault System (CCFS), a group of NE-striking faults. However, the CCFS has not produced any recorded moderate or stronger (>M_W 5.0) earthquakes. Fault properties such as orientation, kinematics, and surface trace length were determined from literature review, geologic fieldworks, and analysis of tectonic geomorphic features. Empirical relations with surface trace lengths were utilized to estimate down-dip width and earthquake magnitude. From these data, a three-dimensional model of the CCFS was created. The model was used to estimate peak ground acceleration (PGA), should an earthquake occur along any of the major faults. Additional PGA corrections were made based on the seismic velocity of the upper 30 meters of the subsurface, extrapolated from the distribution of geologic units from published maps of Metro Cebu. Four major faults were identified, with lengths from 25 to 50 km and capable of generating M_W 6.7 to 7.1 earthquakes. The worst-case earthquake could cause ground motion with intensity IX to X on the PHIVOLCS Earthquake Intensity Scale, equivalent to ≥0.4 g, in 98% of areas within Central Cebu with a population density of >5000/km². Fault dimensions and kinematics were used to calculate static Coulomb stress change caused by the recent strong earthquakes. All major faults in the CCFS were computed to experience an increase in Coulomb stress, ranging from 0.1 to 1.0 bar, from cumulative effects of the recent strong earthquakes. The data suggest that the CCFS may potentially cause devastating damage to central Cebu, the most populated area in the central Philippines. Further investigations on the seismogenesis of the CCFS segments are recommended.

The existence of active fault becomes a source of seismic hazard potential in a particular area that an interesting object of research. In this study, we have been deploying temporary seismograph stations around the Lembang fault which is located about 8 km north of Bandung, West Java, Indonesia. We are trying to find out the subsurface geometry of the Lembang fault using ambient seismic noise tomography. We conduct seismograph stations for 6 months observation from November 2020 to April 2021. We did a design survey by using ray coverage analysis to determine the optimal sensor location to get good ray coverage before the deployment and focus on the Lembang fault lineament. Due to the limited number of sensors that we have, the deployment design of local seismic network for different patterns and a month observation of each pattern. In total, we have 84 points of seismic observation. From the preliminary result of this experiment, we can see a lateral seismic velocity variation in the Lembang fault.

Here we demonstrate the cross correlation of station pairs to extract coherence signal of Rayleigh wave from the ambient seismic noise. 79 seismic stations in Borneo and Sulawesi Islands with 4 months recording (1 September 2020 to 1 Januari 2021) consist of Broadband and Short-Period from BMKG Permanent Seismic Network were used in this study. We applied Python Code – NoisePy to calculate the cross-correlation from daily seismic data in the frequency domain filtered with bandpass at 0.02 – 4 Hz. Then we did waveform stacking to obtain Empirical Green’s Function, and estimated the dispersion curves of group velocity of stations pairs. More than 500 dispersion curves of group velocity were inverted to obtain Rayleigh wave velocity structure beneath Borneo – Sulawesi Region. Our preliminary results are consistent with the geological background of study area. The velocity boundaries show consistent with the faults either in land of Borneo and Sulawesi and also under the sea of Makassar Strait. The low velocity anomalies fairly and clearly observed beneath East Kalimantan that associated with Tertiary Basin.