pure and applied geophysics最新文献

Full waveform inversion (FWI) updates the subsurface model from an initial model by comparing observed and synthetic seismograms. Due to high nonlinearity, FWI is easy to be trapped into local minima. Extended domain FWI, including wavefield reconstruction inversion (WRI) and extended source waveform inversion (ESI) are attractive options to mitigate this issue. This paper makes an in-depth analysis for FWI in the extended domain, identifying key challenges and searching for potential remedies towards practical applications. WRI and ESI are formulated within the same mathematical framework using Lagrangian-based adjoint-state method with a special focus on time-domain formulation using extended sources, while putting connections between classical FWI, WRI and ESI: both WRI and ESI can be viewed as weighted versions of classic FWI. Due to symmetric positive definite Hessian, the conjugate gradient is explored to efficiently solve the normal equation in a matrix free manner, while both time and frequency domain wave equation solvers are feasible. This study finds that the most significant challenge comes from the huge storage demand to store time-domain wavefields through iterations. To resolve this challenge, two possible workaround strategies can be considered, i.e., by extracting sparse frequencial wavefields or by considering time-domain data instead of wavefields for reducing such challenge. We suggest that these options should be explored more intensively for tractable workflows.

During the destruction of the North China Craton in the Mesozoic era, a significant gold mineralization event occurred, leading to the formation of the world-renowned Jiaodong Gold Province. The Liaodong and Jiaodong regions have similar tectonic backgrounds and geological evolution histories. However, the confirmed gold resources in the Liaodong region are only one-tenth of those in Jiaodong. To reveal the controlling factors behind the differences in mineralization between these two regions and explore the deep mineralization prospects in the Liaodong region, we conducted a short-period and high-density array (WSP array) in the Wulong Gold Concentrated Area, the largest goldfield in the Liaodong region. Using data recorded by 334 SmartSolo seismometers for one month, we applied ambient noise tomography to obtain the S-wave velocity structure of the crust down to a depth of 3.5 km beneath the Wulong goldfield. The velocity structure revealed the presence of two sets of low-velocity anomalies trending NNE and NW, respectively, in the shallow crust (shallower than 1.5 km) of the Wulong goldfield, while two high-velocity anomalies were identified at deeper depths (1.5–3.5 km). By combining these findings with the geological characteristics of the Wulong goldfield, it was discovered that the high-velocity anomaly (II) corresponds to the Sanguliu granitic body exposed at the surface, while the high-velocity anomaly (I) could be a concealed intrusive body. The shallow low-velocity anomalies are the result of hydrothermal alteration caused by mineralizing fluids along the NNE- and NW-trending faults. The intersection of these two sets of faults, where the low-velocity anomalies exist, represents the center of the hydrothermal activities. Based on these observations, it is proposed that the area between the Sanguliu granitic body and the concealed intrusive body in the northwest has favorable metallogenic conditions. The intersections of the NNE- and NW-trending faults show the high potential for forming large to super-large altered rock-type gold deposits.

One hundred years ago, Fusakichi Omori died. Our paper is dedicated to his memory. Omori made an outstanding contribution to the physics of earthquakes. In 1894 he formulated the law of aftershock evolution. Omori’s Law states that after the main shock of an earthquake, the frequency of aftershocks decreases hyperbolically with time. In this paper, we briefly describe one of the directions of modern aftershock research. We present Omori’s law in the form of a differential equation describing the evolution of aftershocks. The evolution equation allows us to solve the inverse problem of the earthquake source “cooling down” after the main shock. The solution of the inverse problem allowed us to reveal the existence of the so-called Omori epoch. It is established that at the end of the Omori epoch something similar to a bifurcation of the source state occurs. A logistic equation supposedly describing the bifurcation phenomenon is proposed.

This paper presents the first detailed analysis of grain size parameters and tsunami deposit of the 2018 Anak Krakatau tsunami, considering artificial structures such as buildings and roads. The deposition of tsunamis on land is extremely complex, involving contributions from both the hydrodynamics of tsunami flow propagation and the characteristics of the tsunami, as well as topographical conditions. In both local and detailed contexts, artificial structures can affect the formation of tsunami deposits. In this study, we focused on the effect of artificial structures on the characteristics of the 2018 Anak Krakatau tsunami deposits. Field observations showed that the remains of dikes, houses and asphalt roads significantly influenced the source, thickness, structure of tsunami deposits and grain size parameters. Tsunami deposits consisting of fine-grained material originated from the sediment on the seafloor. Tsunami deposits were thicker in areas closer to the part of the sea unaffected by artificial structures and exhibited a thinning trend inland. In general, the grain size of tsunami deposits is coarser than that of pre-tsunami deposits. Tsunami deposits predominantly exhibit an upward fining trend. Our study explains the key role of artificial structures in the formation of tsunami deposits and the sediment structure produced in coastal areas. A drastic change in the characteristics of the grain size parameters results from the presence of artificial structures. Overall, the tsunami deposit layers could have been better sorted. Significantly different sortation values were observed at sites located above the asphalt road. Similarly, kurtosis values showed an anomaly. The skewness value was inversely proportional to the average grain size in areas affected by artificial structures.

This study highlights significant recent increases in water and air temperatures in the rapidly developing city of Belgrade, Serbia to raise awareness of the anticipated negative impacts and the urgent need to develop appropriate mitigation strategies. We investigate the mean annual water temperature trends at the confluence of the Sava and Danube Rivers, along with air temperature trends at the Belgrade meteorological station, spanning from 1956 to 2020. Results reveal a consistent increase in temperature across all three measuring stations, with the Danube experiencing a rise of 0.34 °C/decade, the Sava at 0.44 °C/decade, and Belgrade's air temperature increasing by 0.39 °C/decade. Employing the Rescaled Adjusted Partial Sums method, sharp rises in water temperature were pinpointed in 1989 for the Sava and 1990 for the Danube, while Belgrade's air temperature surge began in 1998. The highest intensity of air temperature increase within the recent period (1998–2020) was observed at the Belgrade observatory, reaching 0.76 °C/decade. Notably, the Sava exhibited a faster increase in water temperature over the last thirty years compared to the Danube. August marked the peak average water temperature for both rivers, while July recorded the highest average air temperature in Belgrade. Despite differing flow rates, both rivers exhibit similar hydrological regimes, with maximum flows occurring in April and minimum flows in August for the Sava, and October for the Danube. Seasonal temperature increases were most pronounced in summer, notably in August, with the smallest rises occurring during cold periods. Additionally, an inverse proportional relationship between mean annual water temperatures and discharges was observed at both river stations. The overall findings suggest that the increase in both air and water temperatures is more pronounced during the warmer part of the year.

Throughout the geological history of Earth, there have been many changes in the climate system due to natural and external factors. In the past, it can be said that changes in climate were caused by natural causes, while today they are largely caused by human activities. Turkey is among the countries that will be affected by climate change. Therefore, In this study, a stochastic time series model was constructed to forecast the precipitation and temperature data of Turkey between 2020 and 2050. Seasonal Autoregressive Integrated Moving Average models were used to take into account the relationship between the data and seasonality factors. In addition, the most appropriate model for each station was established separately. The accuracy of the predicted data was tested by correlation test (r) and root mean square error (RMSE) test. As a result of the study, the average r value for temperature data was 99% and RMSE value was calculated as 1.46. For precipitation data, the average r value was calculated as 66% and RMSE value as 34.6. In addition, in this study, drought models for Turkey until 2050 were established and spatial and temporal evaluation of these models were made. These models were obtained by analyzing the data of uniformly distributed stations over Turkey between 1990 and 2050 with standard precipitation evapotranspiration index (SPEI). Different time scales (SPEI₃, SPEI₆, SPEI₉ and SPEI₁₂) were used in drought analysis. As a result of this study, drought return interval maps of Turkey and drought maps between 1990 and 2050 were created.

Determining the magnitude of an earthquake rapidly and correctly is essential to starting simulations to evaluate the potential for tsunami generation and early warning for tsunami-prone countries and rapid response, considering countries that lie in seismically active regions. Although the UK does not have a high degree of tsunami hazard, the UK seismic network can estimate the moment magnitude for large earthquakes which will occur around the globe. This study aimed to test the UK Seismological Network Broadband Seismic Stations to calculate the P-wave moment magnitude (M_wp) using teleseismic waves. The standard way to calculate the M_wp is using the P-wave portion of a seismic wave recorded at different epicentral distances. We selected twenty-five seismic events with a magnitude greater than 6.5M_w and epicentral distances between 17 and 90 degrees. The main issue is selecting the P-wave portion of a seismic wave and using a trial P-wave velocity to estimate the M_wp. We simplified the selection of a P-wave portion of seismic waves using a theoretical formula that works with epicentral distance, P-wave arrival time and an apparent P-wave velocity, which calculates the S-wave arrival time. The results show the variation between the Harvard centroid moment tensor (CMT—M_w) and M_wp, which is about ± 0.1 magnitude units in most events and ± 0.2 for some events. These results prove the M_wp technique can be applied to the UK broadband seismic network broadband seismic stations and encourage the use of it immediately following a destructive earthquake anywhere in the world.

Water is a crucial and invaluable natural resource essential for humanity to sustain on Earth. Around 70% of the Earth’s surface is covered by salt water, which has the largest water volume, and just about 2.5% of fresh water is available for human consumption. The factors that control the spatio-temporal variability of these water resources are envisaged to be of importance. Hydrometeorology is the branch of science that deals with water resource management and understanding water availability by simultaneously using the principles of hydrology and meteorology. Extreme hydro-meteorological events like floods, droughts, and other hydro-meteorological calamities are impacting the region’s water resources. For a big state such as Madhya Pradesh, where the availability of hydro-meteorological data is critical in dealing with the management of water resources not only for the state but for the other neighbouring states, those aquifers and rivers are fed by the cross-boundary rivers of the state. Several research activities that have been carried out in Madhya Pradesh in hydrometeorology and allied disciplines by various researchers are reviewed and presented in this paper. This research paper also discussed the analysis of hydrometeorology services and highlighted the significance of hydrometeorology research at regional level. Apart from this, the major challenges faced in hydro-meteorological research in Madhya Pradesh are also highlighted in the paper.

This paper has investigated the impact of convective parameterization schemes (CPS) and land surface models (LSM) on the simulation of summer climate over the Democratic People’s Republic of Korea (DPR Korea) using the regional climate model (RegCM 4.7). The sensitivity experiments with two LSMs [Biosphere Atmosphere Transfer Scheme (BATS) and Community Land Model (CLM 3.5)] and four CPSs (Grell, Emanuel, Grell over land and Emanuel over ocean (GL_EO), Emanuel over land and Grell over ocean (EL_GO)) at 30 km horizontal resolution are carried out in summer (from June to August) for 10 years (2001–2010) for this purpose. The simulation results are compared with the available observation data provided from the State Hydro-Meteorological Administration of the DPR Korea (SHMAK). The results show that summer mean circulation patterns (SMCP) and summer averaged surface temperature (SAST) is well captured for most of the simulations, but summer rainfall is not well represented by RegCM 4.7. The performance of the CLM3.5 scheme is better in all the simulations than the BATS scheme. Among the CPSs, the EL_GO scheme shows the smallest biases in the simulation of SAST and summer rainfall. The simulations using EL_GO with CLM3.5 shows the best performance in simulating the SAST and summer rainfall over the study region among the considered CPSs and LSMs. These results will be helpful to improve the prediction of climate change over the DPR Korea.