Seismic Moment Tensor Solutions from GeoNet Data to Provide a Moment Magnitude Scale for New Zealand

<p>The aim of this project is to enable accurate earthquake magnitudes (moment magnitude, MW) to be calculated routinely and in near real-time for New Zealand earthquakes. This would be done by inversion of waveform data to obtain seismic moment tensors. Seismic moment tensors also provide information on fault-type. I use a well-established seismic moment tensor inversion method, the Time-Domain [seismic] Moment Tensor Inversion algorithm (TDMT_INVC) and apply it to GeoNet broadband waveform data to generate moment tensor solutions for New Zealand earthquakes. Some modifications to this software were made. A velocity model can now be automatically used to calculate Green's functions without having a pseudolayer boundary at the source depth. Green's functions can be calculated for multiple depths in a single step, and data are detrended and a suitable data window is selected. The seismic moment tensor solution that has either the maximum variance reduction or the maximum double-couple component is automatically selected for each depth. Seismic moment tensors were calculated for 24 New Zealand earthquakes from 2000 to 2005. The Global CMT project has calculated CMT solutions for 22 of these, and the Global CMT project solutions are compared to the solutions obtained in this project to test the accuracy of the solutions obtained using the TDMT_INVC code. The moment magnitude values are close to the Global CMT values for all earthquakes. The focal mechanisms could only be determined for a few of the earthquakes studied. The value of the moment magnitude appears to be less sensitive to the velocity model and earthquake location (epicentre and depth) than the focal mechanism. Distinguishing legitimate seismic signal from background seismic noise is likely to be the biggest problem in routine inversions.</p>

Seismic Moment Tensor Solutions from GeoNet Data to Provide a Moment Magnitude Scale for New Zealand

<p>The aim of this project is to enable accurate earthquake magnitudes (moment magnitude, MW) to be calculated routinely and in near real-time for New Zealand earthquakes. This would be done by inversion of waveform data to obtain seismic moment tensors. Seismic moment tensors also provide information on fault-type. I use a well-established seismic moment tensor inversion method, the Time-Domain [seismic] Moment Tensor Inversion algorithm (TDMT_INVC) and apply it to GeoNet broadband waveform data to generate moment tensor solutions for New Zealand earthquakes. Some modifications to this software were made. A velocity model can now be automatically used to calculate Green's functions without having a pseudolayer boundary at the source depth. Green's functions can be calculated for multiple depths in a single step, and data are detrended and a suitable data window is selected. The seismic moment tensor solution that has either the maximum variance reduction or the maximum double-couple component is automatically selected for each depth. Seismic moment tensors were calculated for 24 New Zealand earthquakes from 2000 to 2005. The Global CMT project has calculated CMT solutions for 22 of these, and the Global CMT project solutions are compared to the solutions obtained in this project to test the accuracy of the solutions obtained using the TDMT_INVC code. The moment magnitude values are close to the Global CMT values for all earthquakes. The focal mechanisms could only be determined for a few of the earthquakes studied. The value of the moment magnitude appears to be less sensitive to the velocity model and earthquake location (epicentre and depth) than the focal mechanism. Distinguishing legitimate seismic signal from background seismic noise is likely to be the biggest problem in routine inversions.</p>

Earthquake Magnitude Estimation using Precise Point Positioning

An accurate estimation of an earthquake magnitude plays an important role in targeting emergency services towards affected areas. Along with the traditional methods using seismometers, site displacements caused by an earthquake can be monitored by the Global Navigation Satellite Systems (GNSS). GNSS can be used either in real-time for early warning systems or in offline mode for precise monitoring of ground motion. The Precise Point Positioning (PPP) offers an optimal method for such purposes, because data from only one receiver are considered and thus not affected by other potentially not stable stations. Precise external products and empirical models have to be applied, and the initial convergence can be reduced or eliminated by the backward smoothing strategy or integer ambiguity resolution. The product for the magnitude estimation is a peak ground displacement (PGD). PGDs observed at many GNSS stations can be utilized for a robust estimate of an earthquake magnitude. We tested the accuracy of estimated magnitude scaling when using displacement waveforms collected from six selected earthquakes between the years 2016 and 2020 with magnitudes in a range of 7.5–8.2 Moment magnitude MW. We processed GNSS 1Hz and 5Hz data from 182 stations by the PPP method implemented in the G-Nut/Geb software. The precise satellites orbits and clocks corrections were provided by the Center for Orbit Determination in Europe (CODE). PGDs derived on individual GNSS sites formed the basis for ground motion parameters estimation. We processed the GNSS observations by the combination of the Kalman filter (FLT) and the backward smoother (SMT), which significantly enhanced the kinematic solution. The estimated magnitudes of all the included earthquakes were compared to the reference values released by the U. S. Geological Survey (USGS). The moment magnitude based on SMT was improved by 20% compared to the FLT-only solution. An average difference from the comparison was 0.07 MW and 0.09 MW for SMT and FLT solutions, respectively. The corresponding standard deviations were 0.18 MW and 0.22 MW for SMT and FLT solutions, which shows a good consistency of our and the reference estimates.

Application of P-Wave Moment Magnitude (Mwp) and Rupture Time Duration (Tdur) to Analyze A Potential Tsunami Earthquake in Sumatra

Tsunami warning is one of many important reports to save lives and reduce the damage for local peoples. A moment magnitude of P-wave (Mwp) and the rupture time duration (Tdur) can be used as the quickly parameters to diseminate the tsunami warning. In this paper, we analyze the seismic waveform from global network to get Mwp and Tdur of South-West Coast of Sumatera earthquake. Mwp was calculated using automatic and manual phase picking of P phase. The results of this study show a well-analyzed relationship between P wave from automatic and manual picking, Mwp and time duration, respectively. The result also give an encouraging studies for the early warning system that will be set up in the future in the region.

Penyuluhan Kesehatan Tentang Prosedur Evakuasi Saat Terjadinya Gempa Bumi Di Desa Wonorejo Karanganyar

Earthquakes in Indonesia cause physical damage as well as fatalities, high mortality rates and disability when an earthquake occurs, it is necessary to reduce or prevent it by increasing people's knowledge and skills about how to evacuate during an earthquake. Earthquakes that are not resolved with resilience and lack of human resources that can handle earthquakes from pre-disaster, during disaster and post-disaster. Earthquakes are caused by the movement of the Earth's crust (Earth's plates). The frequency of a region, refers to the type and size of earthquakes experienced over a period of time. Earthquakes are measured using a seismometer. Moment magnitude is the most common scale where earthquakes occur throughout the world so that the community is demanded to be prepared, one of which is evacuation during a disaster which is held by evacuation counseling in Wonorejo Village, Karanganyar. earthquake with pre-test data 75% of the residents did not know and after counseling and post-testing it was found that 90% of the residents understood the skills and knowledge of evacuation during an earthquake. with the lack of knowledge and skills of residents regarding evacuation during an earthquake, it is very appropriate for residents to understand when an earthquake occurs

Ground-motion models for Vrancea intermediate-depth earthquakes

A newly compiled high-quality ground-shaking dataset of 207 intermediate-depth earthquakes recorded in the Vrancea region of the south-eastern Carpathian mountains in Romania was used to develop region-specific empirical predictive equations for various intensity measures: peak ground acceleration, peak ground velocity, and 5%-damped pseudo-spectral acceleration up to 10 s. Besides common predictor variables (e.g. moment magnitude, depth, hypocentral distance, and site conditions), additional distance scaling parameters were added to describe the specific attenuation pattern observed at the stations located not only on the back and fore but also along the Carpathian arc. In this model, we introduce a proxy measure for the site as the fundamental frequency of resonance to characterize the site response at each recording seismic station beside the soil classes. To additionally reduce the site-to-site variability, a non-ergodic methodology was considered, resulting in a lower standard deviation of about 25%. Statistical evaluation of the newly proposed ground-motion models indicates robust performance compared to regional observations. The model shows significant improvements in describing the spatial variability (at different spectral ordinates), particularly for the fore-arc area of the Carpathians where a deep sedimentary basin is located. Furthermore, the model presented herein improves estimates of ground shaking at longer spectral ordinates (>1 s) in agreement with the observations. The proposed ground-motion models are valid for hypocentral distances less than 500 km, depths over 70 km and within the moment magnitude range of 4.0–7.4.

Konversi Empiris Summary Magnitude, Local Magnitude, Body-Wave Magnitude, Surface Magnitude, dan Moment Magnitude Menggunakan Data Gempabumi 1922-2020 di Nusa Tenggara Barat

The existence of magnitude type variation from existing earthquake catalogue sources show that uniforming process is necessary. Beside that these type of magnitude will saturates in certain value, which are different with moment magnitude (Mw) which is not saturated and can describe earthquake process better. Our research initially did compatibility test between summary magnitude which is largely used by BMKG with other magnitude type. Furthermore, the purpose of our research is determination of empirical relation between magnitude type summary magnitude (M), local magnitude (ML), body-wave magnitude (mb), dan surface magnitude (Ms) which are usually used by earthquake catalogues to Mw. Method used in this research is linear regression using data set from BMKG, ISC-EHB, USGS, and Global CMT catalogues with are limited in West Nusa Tenggara and surrounding area. Data used in this research contains of 24.703 earthquake events during period May 9th 1922 until June 27th 2020. The result of this research shows there was good relation between M magnitude type with others magnitude type. Our research also found a conversion formula of M, ML, MLv, mb, and Ms to Mw with well-defined correlation.

Earthquakes of 1838 and 1839 in the Slovene Hills (Slovenia)-Međimurje (Croatia) area

Analyses of available data (newspaper reports, historical and church chronicles, chronical earthquake overviews, travel books, monographies, research papers, etc.) on effects of the earthquakes that shook the greater Ormož area at the Slovenian-Croatian border in the 1838 and 1839 revealed that one of them, recorded in a number of regional and global catalogues, is in fact a fake - the earthquake of 26 August 1838 never happened. This error creeped into various reports and studies, and then into many relevant catalogues, so this event should by systematically erased from the catalogues used to estimate seismicity rates in the neighbourhoods of north-western Croatia, north-eastern Slovenia, and south-western Hungary.Regarding the earthquake of 31 July 1838, we used important new sources of information that have not been consulted in any previous study. This made inversion of macroseismic parameters more robust. Our estimates of the macroseismic moment magnitude (Mwm = 4.8) is mostly higher than the values reported in the available catalogues. Reliable information on the effects of the smaller event of 22 March 1839 were found for two localities only, so its epicentre was placed into the town of Ormož where the maximum intensity was observed. Its estimated moment magnitude (Mwm) is close to the median of values found in the six consulted catalogues that listed this event.The macroseismic epicentre of the 1838 earthquake lies close to the junction of surface traces of the Donat strike-slip fault and the reverse Čakovec fault. Based on their assumed geometry and the location of the macroseismic hypocentre, we give slight preference to the Donat fault as the seismogenic source.

Comprehensive Characterization and Mitigation of Hydraulic Fracturing-Induced Seismicity in Fox Creek, Alberta

Summary The relationships among formation properties, fracturing operations, and induced earthquakes nucleated at distinctive moments and positions remain unclear. In this study, a complete data set on formations, seismicity, and fracturing treatments is collected in Fox Creek, Alberta, Canada. The data set is then used to characterize the induced seismicity and evaluate its susceptibility toward fracturing stimulations via integration of geology, geomechanics, and hydrology. Five mechanisms are identified to account for spatiotemporal activation of the nearby faults in Fox Creek, where all major events [with a moment magnitude (Mw) greater than 2.5] are caused by the increase in pore pressure and poroelastic stress during the fracturing operation. In addition, an integrated geological index (IGI) and a combined geomechanical index (CGI) are first proposed to indicate seismicity susceptibility, which is consistent with the spatial distribution of induced earthquakes. Finally, mitigation strategy results suggest that enlarging a hydraulic fracture-fault distance and decreasing a fracturing job size can reduce the risk of potential seismic activities.

3D linked megathrust, dynamic rupture and tsunami propagation and inundation modeling: Dynamic effects of supershear and tsunami earthquakes

&lt;p&gt;Earthquake rupture dynamic models capture the variability of slip in space and time while accounting for the structural complexity which is characteristic for subduction zones. The use of a geodynamic subduction and seismic cycling (SC) model to initialize dynamic rupture (DR) ensures that initial conditions are self-consistent and reflect long-term behavior. We extend the 2D geodynamical subduction and SC model of van Zelst et al. (2019) and use it as input for realistic 3-dimensional DR megathrust earthquake models. We follow the subduction to tsunami run-up linking approach described in Madden et al. (2020), including a complex subduction setup along with their resulting tsunamis. The distinct variation of shear traction and friction coefficients with depth lead to realistic average rupture speeds and dynamic stress drop as well as efficient tsunami generation.&amp;#160;&lt;/p&gt;&lt;p&gt;We here analyze a total of 14 subduction-initialized 3D dynamic rupture-tsunami scenarios. By varying the hypocentral location along arc and depth, we generate 12 distinct unilateral and bilateral earthquakes with depth-variable slip distribution and directivity, bimaterial, and geometrical effects in the dynamic slip evolutions. While depth variations of the hypocenters barely influence the tsunami behavior, lateral varying nucleation locations lead to a shift in the on-fault slip which causes time delays of the wave arrival at the coast. The fault geometry of our DR model that arises during the SC model is non-planar and includes large-scale roughness. These features (topographic highs) trigger supershear rupture propagation in up-dip or down-dip direction, depending on the hypocentral depth.&lt;/p&gt;&lt;p&gt;In two additional scenarios, we analyze variations in the energy budget of the DR scenarios. In the SC model, an incompressible medium is assumed (&amp;#957;=0.5) which is valid only for small changes in pressure and temperature. Unlike in the DR model where the material is compressible and a different Poisson&amp;#8217;s ratio (&amp;#957;=0.25) has to be assigned. Poisson&amp;#8217;s ratios between 0.1 and 0.4 stand for various compressible materials. To achieve a lower shear strength of all material on and off the megathrust fault and to facilitate slip, we increase the Poisson ratio in the DR model to &amp;#957;=0.3 which is consistent with basaltic rocks. As a result, larger fault slip is concentrated at shallower depths and generates higher vertical seafloor displacement and earthquake moment magnitude respectively. Even though the tsunami amplitudes are much higher, the same dynamic behavior as in the twelve hypocenter-variable models can be observed. Lastly, we increase fracture energy by changing the critical slip distance in the linear slip-weakening frictional parameterization. This generates a tsunami earthquake (Kanamori, 1972) characterized by low rupture velocity (on average half the amount of s-wave speed) and low peak slip rate, but at the same time large shallow fault slip and moment magnitude. The shallow fault slip of this event causes the highest vertical seafloor uplift compared to all other simulations. This leads to the highest tsunami amplitude and inundation area while the wavefront hits the coast delayed compared to the other scenarios.&lt;/p&gt;