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Seismologists and geoscientists often need earthquake catalogues for various types of research. This input usually contains basic earthquake parameters such as location (longitude, latitude, depth, and origin time), as well as magnitude information. For the latter, the moment magnitude Mw has become the most sought after magnitude scale in the seismological community to characterize the size of an earthquake. In this contribution we provide an informative account of the Mw content for the newly rebuilt Bulletin of the International Seismological Centre (ISC, http://www.isc.ac.uk, last access: May 2021), which is regarded as the most comprehensive record of the Earth's seismicity. From this data, we extracted a list of hypocentres with Mw from a multitude of agencies reporting data to the ISC. We first summarize the main temporal and spatial features of the Mw provided by global (i.e. providing results for moderate to great earthquakes worldwide) and regional agencies (i.e. also providing results for small earthquakes in a specific area). Following this, we discuss their comparisons, by considering not only Mw but also the surface wave magnitude MS and short-period body wave magnitude mb. By using the Global Centroid Moment Tensor solutions as an authoritative global agency, we identify regional agencies that best complement it and show examples of frequency–magnitude distributions in different areas obtained both from the Global Centroid Moment Tensor alone and complemented by Mw from regional agencies. The work done by the regional agencies in terms of Mw is fundamental to improve our understanding of the seismicity of an area, and we call for the implementation of procedures to compute Mw in a systematic way in areas currently not well covered in this respect, such as vast parts of continental Asia and Africa. In addition, more studies are needed to clarify the causes of the apparent overestimation of global Mw estimations compared to regional Mw. Such difference is also observed in the comparisons of Mw with MS and mb. The results presented here are obtained from the dataset (Di Giacomo and Harris, 2020, https://doi.org/10.31905/J2W2M64S) stored at the ISC Dataset Repository (http://www.isc.ac.uk/dataset_repository/, last access: May 2021).

All nuclear explosions are banned by the Comprehensive Nuclear-Test-Ban Treaty. In the context of the treaty a verification regime was put into place to detect, locate, and characterize nuclear explosions at any time, by anyone and everywhere on the Earth. The International Monitoring System, which plays a key role in the verification regime, was set up by the Preparatory Commission of the Comprehensive Nuclear-Test-Ban Treaty Organization. Out of the several different monitoring techniques applied in the International Monitoring System the seismic waveform approach is the most effective and reliable technology for monitoring nuclear explosions underground. This study introduces a deterministic method of threshold monitoring that allows to asses a lower body wave magnitude limit of a potential seismic event in a certain geographical region, that can be detected by those seismic stations being part of the International Monitoring System network. The method is based on measurements of ambient seismic noise levels at the individual seismic stations along with global distance corrections terms for the body wave magnitude. The results suggest that an average global detection capability of approximately body wave magnitude 4.0 can be achieved using only stations from the primary seismic network of the International Monitoring System. The incorporation of seismic stations from the auxiliary seismic network leads to a slight improvement of the detection capability, while the use and analysis of wave arrivals from distances greater than 120∘ results in a significant improvement of the detection capability. Temporal variations in terms of hourly and monthly changes of the global detection capability can not be observed. Overall, comparisons between detection capability and manually retrieved body wave magnitudes from the Reviewed Event Bulletin suggest, that our method yields a more conservative estimation of the detection capability and that in reality detection thresholds might be even lower than estimated., Bundesanstalt für Geowissenschaften und Rohstoffe (BGR) (4230)

An earthquake catalog based on a unified magnitude scale is an important prerequisite for analyses of seismic activities and seismic hazards. To unify the magnitude scales of earthquakes in China’s seas and neighboring regions, we developed conversion relationships between surface- and body-wave magnitudes and the global centroid moment tensor (GCMT) and National Research Institute for Earth Science and Disaster Resilience (NIED) moment magnitudes for shallow and intermediate- and deep-focus earthquakes in China’s seas and adjacent areas. We employed data collected by the Chinese Earthquake Network Center, GCMT, and NIED for earthquakes of magnitude 4.5 and higher in China’s seas and neighboring regions from 1976 to 2018. We used the linear least squares regression method and the orthogonal regression method to fit the seismic data under different magnitude ranges and different focal depth ranges. The results provided empirical formulas to unify magnitude scales for the earthquakes in China’s seas and neighboring regions and also provided an important basis for seismic catalog integrity analyses and seismic activity studies for this area. The results are significant for seismic hazard analyses, seismic zoning, and mid- and long-term forecast analyses of seismic activities in the area.

SUMMARYWe explore the possible theoretical origin of the distance–depth correction q(Δ, h) introduced 75 yr ago by B. Gutenberg for the computation of the body-wave magnitude mb, and still in use today. We synthesize a large data set of seismograms using a modern model of P-wave velocity and attenuation, and process them through the exact algorithm mandated under present-day seismological practice, to build our own version, qSO, of the correction, and compare it to the original ones, q45 and q56, proposed by B. Gutenberg and C.F. Richter. While we can reproduce some of the large scale variations in their corrections, we cannot understand their small scale details. We discuss a number of possible sources of bias in the data sets used at the time, and suggest the need for a complete revision of existing mb catalogues.

Seismologists and geoscientists in general often need earthquake catalogues for various types of research. This input usually contains basic earthquake parameters such as location (longitude, latitude, depth and origin time) as well as magnitude information. For the latter, the moment magnitude Mw has became the most sought after magnitude scale in the seismological community to characterize the size of an earthquake. In this contribution we provide an informative account of the Mw content for the newly rebuilt Bulletin of the International Seismological Centre (ISC, http://www.isc.ac.uk/), which is regarded as the most comprehensive record of the Earth's seismicity. From it, we extracted a list of hypocentres with Mw from a multitude of agencies reporting data to the ISC. We first summarize the main temporal-spatial features of the Mw provided by global agencies (i.e., providing results for moderate to great earthquakes worldwide) and regional ones (i.e., also providing results or small earthquakes in a specific area). Then we discuss their comparisons, not only by considering Mw but also the surface wave magnitude MS and short-period body wave magnitude mb. By using the Global Centroid Moment Tensor solutions as authoritative global agency, we identify regional agencies that best complement it and show examples of frequency-magnitude distributions in different areas obtained both from the Global Centroid Moment Tensor alone and complemented by Mw from regional agencies. The work done by the regional agencies in terms of Mw is fundamental to improve our understanding of the seismicity of an area and we call for the implementation of procedures to compute Mw in a systematic way in areas currently not well covered in this respect, such as vast parts of continental Asia and Africa. In addition, more studies are needed to clarify the causes of the apparent overestimation of global Mw estimations compared to regional Mw. Such difference is also observed in the comparisons of Mw with MS and mb. The results presented here are obtained from the dataset (Di Giacomo and Harris, 2020, https://doi.org/10.31905/J2W2M64S) stored at the ISC Dataset Repository (http://www.isc.ac.uk/dataset_repository/).

The study of the stress-strain state of a medium in seismically quiet areas is difficult because of the absence of strong events. Under such circumstances, each earthquake, even relatively weak, is of high importance. In this case, all possible information on tectonic stresses and their dynamics, e.g., information on time, location, and magnitude of aftershocks, should be obtained from available seismic data. The earthquake near the town of Mariupol which occurred on August 7, 2016, had a body wave magnitude of 4.5–4.9 from the data of the different seismological centers. We detected 12 aftershocks that occurred within 5 days after the main shock using two seismic arrays (AKASG and BRTR) and one three-component station (KBZ) of the International Monitoring System, as well as two array stations of the Institute of Geosphere Dynamics, Russian Academy of Sciences. For six aftershocks, signals were found at three or more stations. The other aftershocks were detected from the data at two out of three nearest stations. Signal detection and association with aftershocks of the main shock, as well as estimation of magnitude and relative location of the found aftershocks, were carried out using the method of waveform cross-correlation (WFCC). The signals from the main shock that acted as the only master event (ME) for the WFCC method were used as waveform templates. To increase the signal-to-noise ratio and to determine the exact onset time of regular seismic waves from aftershocks, we used waveform templates of different length, from 10 to 180 s depending on the wave type and distance to the station, as well as band filtering in narrow frequency bands. The highest sensitivity of the detector and accuracy of the P-wave onset time estimates were reached when a waveform template included all regular waves from P to L g . Association of signals with aftershocks was based on back projection of signal arrival times to origin times using the travel time from a master event to the station, which was measured with a very low error, being equal to almost half of the digitization step length. To develop a seismic event hypothesis, the origin times at two or more stations should be spaced within a 2-s interval.

The earthquake magnitude data for Sudan Territory includes four types of magnitude scales (Moment Magnitude Mw, Surface wave magnitude Ms, Local magnitude ML and Body wave Magnitude mb ). Unifying the magnitude scale of the compiled earthquake catalogue requires converting these scales to one appropriate scale, usually moment magnitude scale. Therefore, the current paper is presented to retrieve plausible magnitude regression relationships for Sudan Territory. For this reason, all earthquakes that reported by Mw and any other type of magnitude scale are separated and used to derive the earthquake magnitude regression relationships for studied area. The conversion equations are derived using three types of regressions; the standard least-square regression, the inverted standard least-square regression and the particular orthogonal regression. The residual analysis and the log-likelihood method are performed to judge the goodness of fit for each model. The analysis indicated that the models derived by the standard least-square regression for each data-set are well represent the magnitude data within the study area followed by those yielded by the orthogonal regression.

We propose a P wave based procedure for the rapid estimation of the radiated seismic energy, and a novel relationship for obtaining an energy-based local magnitude (MLe) measure of the earthquake size. We apply the new procedure to the seismic sequence that struck Central Italy in 2016. Scaling relationships involving seismic moment and radiated energy are discussed for the Mw 6.0 Amatrice, Mw 5.9 Ussita, and Mw 6.5 Norcia earthquakes, including 35 ML > 4 aftershocks. The Mw 6.0 Amatrice earthquake shows the highest apparent stress, and the observed differences among the three main events highlight the dynamic heterogeneity with which large earthquakes can occur in Central Italy. Differences between estimates of MLe and Mw allows identification of events which are characterized by a higher proportion of energy being transferred to seismic waves, providing important real-time indications of earthquakes shaking potential.

The earthquake early warning (EEW) system is difficult to provide consistent magnitude estimate in the early stage of an earthquake occurrence because only few stations are triggered and few seismic signals are recorded. One of the feasible methods to measure the size of earthquakes is to extract amplitude parameters using the initial portion of the recorded waveforms after P-wave arrival. However, for a large-magnitude earthquake (M w > 7.0), the time to complete the whole ruptures resulted from the corresponding fault may be very long. The magnitude estimations may not be correctly predicted by the initial portion of the seismograms. To estimate the magnitude of a large earthquake in real-time, the amplitude parameters should be updated with ongoing waveforms instead of adopting amplitude contents in a predefined fixed-length time window, since it may underestimate magnitude for large-magnitude events. In this paper, we propose a fast, robust and less-saturated approach to estimate earthquake magnitudes. The EEW system will initially give a lower-bound of the magnitude in a time window with a few seconds and then update magnitude with less saturation by extending the time window. Here we compared two kinds of time windows for measuring amplitudes. One is P-wave time window (PTW) after P-wave arrival; the other is whole-wave time window after P-wave arrival (WTW), which may include both P and S wave. One to ten second time windows for both PTW and WTW are considered to measure the peak ground displacement from the vertical component of the waveforms. Linear regression analysis are run at each time step (1- to 10-s time interval) to find the empirical relationships among peak ground displacement, hypocentral distances, and magnitudes using the earthquake records from 1993 to 2012 in Taiwan with magnitude greater than 5.5 and focal depth less than 30 km. The result shows that considering WTW to estimate magnitudes has smaller standard deviation than PTW. The magnitude estimations using 1-s time widow have larger uncertainties. Progressively adopting peak displacement amplitudes (P d ) from 2- to 10-s WTW is suggested for EEW systems.

A weak seismic event with body wave magnitude 2.1 was detected near the epicenter of an underground explosion conducted by the Democratic People’s Republic of Korea (DPRK) on September 9, 2016. The event occurred approximately two days after the test. Using the method of waveform cross-correlation, two array stations of the International Monitoring System (IMS), USRK and KSRS, recorded the arrival of P n waves. At the same time, this event was not recorded during the standard automatic processing at the International Data Center. The location and other characteristics of this weak event indicate that it is likely to have been an aftershock of the preceding explosion. Based on the successful automatic detection and construction of the event, we conducted an extended investigation, which consisted in searching for secondary seismic phases at the nearest stations that do not belong to the International Monitoring System. The final solution, which is based on waveform cross-correlation, includes stations MDJ (China) and SEHB (Republic of Korea), the aftershock epicenter is located at ~2 km northwest of the epicenter of the DPRK test.

The article proves the application of short-period sensors with extended frequency response as a reasonable alternative to broadband seismometers. We assessed uncertainties between magnitudes determined by short-period and broadband sensor data for earthquakes with M > 6 recorded at the Mikhnevo geophysical observatory in 2014. Data analysis consisted of body wave magnitude and surface wave magnitude estimates by standard seismological methods. Magnitude errors corresponded to the magnitude uncertainties in seismological catalogs.

Seismological characteristics of the North Korean largest nuclear test of September 2017 have been examined using the data of the In− dian Seismological Network. Full waveform modelling of the ground motion data of Indian stations for this nuclear test shows 16% isotropic component, 47.5% DC and 35.8% CLVD components. The Indian stations being located about 3500 to 5000 km away from the source, gave lesser isotropic component as compared to that from the nearby stations around the North Korean test site. This is attributed to the rapid attenuation of the high frequencies emitted from the source. Its average body wave magnitude, mb from the Indian stations broadly agrees with that reported by worldwide data. It was found that the surface wave magnitude of this test in North Korea was large as com− pared to those from the Kazakistan and Nevada nuclear tests for almost similar mb. It is hypothesized that more powerful fusion pro− cess in the nuclear test could result in larger tectonic slip.

On 3 September 2017 official channels of the Democratic People's Republic of Korea announced the successful test of a thermonuclear device. Only seconds to minutes after the alleged nuclear explosion at the Punggye-ri nuclear test site in the mountainous region in the country's northeast at 03:30:02 (UTC), hundreds of seismic stations distributed all around the globe picked up strong and distinct signals associated with an explosion. Different seismological agencies reported body wave magnitudes of well above 6.0, consequently estimating the explosive yield of the device on the order of hundreds of kT TNT equivalent. The 2017 event can therefore be assessed as being multiple times larger in energy than the two preceding North Korean events in January and September 2016. This study provides a multi-technology analysis of the 2017 North Korean event and its aftermath using a wide array of geophysical methods. Seismological investigations locate the event within the test site at a depth of approximately 0.6 km below the surface. The radiation and generation of P- and S-wave energy in the source region are significantly influenced by the topography of the Mt. Mantap massif. Inversions for the full moment tensor of the main event reveal a dominant isotropic component accompanied by significant amounts of double couple and compensated linear vector dipole terms, confirming the explosive character of the event. The analysis of the source mechanism of an aftershock that occurred around 8 min after the test in the direct vicinity suggest a cavity collapse. Measurements at seismic stations of the International Monitoring System result in a body wave magnitude of 6.2, which translates to an yield estimate of around 400 kT TNT equivalent. The explosive yield is possibly overestimated, since topography and depth phases both tend to enhance the peak amplitudes of teleseismic P waves. Interferometric synthetic aperture radar analysis using data from the ALOS-2 satellite reveal strong surface deformations in the epicenter region. Additional multispectral optical data from the Pleiades satellite show clear landslide activity at the test site. The strong surface deformations generated large acoustic pressure peaks, which were observed as infrasound signals with distinctive waveforms even at distances of 401 km. In the aftermath of the 2017 event, atmospheric traces of the fission product 133Xe were detected at various locations in the wider region. While for 133Xe measurements in September 2017, the Punggye-ri test site is disfavored as a source by means of atmospheric transport modeling, detections in October 2017 at the International Monitoring System station RN58 in Russia indicate a potential delayed leakage of 133Xe at the test site from the 2017 North Korean nuclear test.

Nonlinear behaviors of a free-floating body in waves were experimentally investigated in the present study. The experiments were carried out for 6 different wave heights and 6 different wave periods to cover a relatively wide range of wave nonlinearities. A charge-coupled device (CCD) camera was used to capture the real-time motion of the floating body. The measurement data show that the sway, heave and roll motions of the floating body are all harmonic oscillations while the equilibrium position of the sway motion drifts in the wave direction. The drift speed is proportional to wave steepness when the size of the floating body is comparable to the wavelength, while it is proportional to the square of wave steepness when the floating body is relatively small. In addition, the drift motion leads to a slightly longer oscillation period of the floating body than the wave period of nonlinear wave and the discrepancy increases with the increment of wave steepness.

Recently, the world has experienced an increased number of major earthquakes. The Zagros belt is among the most seismically active mountain ranges in the world. Due to Kuwait's location in the southwest of the Zagros belt, it is affected by relative tectonic movements in the neighboring region. It is vital to assess the Zagros seismic risks in Kuwait using recent data and coordinate with the competent authorities to reduce those risks. Using the body wave magnitude (Mb) data collected in Kuwait, we want to assess the recent changes in the magnitude of earthquakes and its variations in Kuwait's vicinity. We built a change point model to detect the significant changes in its parameters. This paper applies a hierarchical Bayesian technique and derives the marginal posterior density function for the Mb. Our interest lies in identifying a shift in the mean of a single or multiple change points as well as the changes in the variation. Building upon the model and its parameters for the 2002–2003 data, we...

A homogeneous earthquake catalogue for Greece and adjacent areas covering the period 1900–2009 is presented, to be used for reliable seismic hazard studies. The catalogues of Makropoulos and Burton (1981) and Makropoulos et al. (1989), covering the time span 1900–1985, were updated for the period 1986–2009 using instrumentally determined focal coordinates, except for the magnitude from the bulletin of the ISC. For Ms, which is the magnitude scale included in the previous versions, the same procedure applied since 1964 was adopted, using the ISC body wave magnitude (mb) and a regression equation. In the present update, Mw is also calculated for the entire period 1900–2009 using a formula derived from all available moment magnitudes and directly determined by the moment tensor inversion method. Thus, a magnitude homogeneous catalogue concerning both Ms and Mw scales is presented. The extended catalogue contains 7352 events, 70% more than the 4310 events of the previous published (1989) version. The completeness test revealed that the catalogue is complete for magnitudes above 4 for the last 34 yr and that no earthquake with magnitude 6 or greater has been omitted in the whole instrumental era (1900–2009).

After Cairo Earthquake in 1992 (Ms 5.9), the government established the Egyptian National Seismological Network (ENSN) organized by the National Research Institute of Astronomy and Geophysics (NRIAG) start to work since 1997; NRIAG has a real monitoring of the seismological activity in and around different parts of Egypt. A selected 5000 events from the ENSN annual bulletin in the period 2004–2013 with calculated local magnitude (M L) based on Richter regular formula was used in this study; a duration magnitude was calculated for these events and regressed with M L. Another aim of this study is to develop a regression relation of the calculated body wave magnitude (M b) to the unified moment magnitude (M w) which is the base for homogenization of earthquake catalogue needed for seismic hazard studies. Standard least square regression usually fails to give reliable results when both regressed variables have measurement errors; orthogonal standard regression (OSR) is the most reliable tool used for conversion of observed M b values with the moment magnitude M w. The accuracy of the resulting relations from regression have been checked with another 20 events of the data and shows the advantage of using OSR method to get regressed relation to homogenize any catalogue containing various magnitudes with measurement errors, by their regression with a Mw. The proposed procedure also remains valid in case the magnitudes have measurement errors different from unity.

Sumatra has three sources of earthquakes, these are subduction zone, Sumatra fault system and outer arc faults which are very closed to settlements so these pose serious threat to human lives also properties. Earthquake early warning system should be developed for mitigation. This study aims to developing earthquake early warning system by way of estimating the magnitude before the arrival of S waves. The magnitude is estimated from relationship between τc parameter and magnitude. Strong ground motion record were integrated twice to get the displacement record with high-pass Butterworth filter applied. τc was determined from ratio of displacement and velocity of vertical component record. τc reflects the size of an earthquake from initial portion of the P waves. τc method could generate magnitude estimation with 0.71 deviation value from actual size impending earthquake, with 0,5 of corner frequency and needed 21,1 second before the arrival of S waves. This method validated with the existing earthquake ca...

The U.S. Geological Survey National Earthquake Information Center (NEIC) uses a variety of classical network‐averaged magnitudes (e.g., m b and M s) and waveform modeling procedures to determine the moment magnitude ( M w) of an earthquake from teleseismic observations. Initial magnitude estimates are often inaccurate because of poor azimuthal control (sampling of the focal sphere) and/or intrinsic limitation of each method to a specific range of event size. To provide faster and more accurate estimates of the moment magnitude, source duration, and source complexity, NEIC is exploring the use of a variation of the empirical Green’s function (EGF) deconvolution procedure. This approach uses a predicted focal mechanism derived from the Global Centroid Moment Tensor Catalog to compute teleseismic P ‐wave synthetic seismograms, which are then deconvolved from observed P and SH waveforms to determine station‐specific M w, source time function, and a network‐averaged M w. Our EGF approach is validated using broadband waveforms from 246 earthquakes in the magnitude range M w 6.0–9.1. Within approximately 13 min of earthquake origin time, our procedure using teleseismic P waves only computes an M w that lies within ±0.25 of the final W ‐phase M w in the magnitude range 6–8. Using later arriving teleseismic SH phases results in an M w that lies within ±0.12 of the W ‐phase M w. For magnitude 8 or larger earthquakes, we underestimated the moment magnitude by up to 0.8 magnitude units, primarily due to the initial P phase not containing the total seismic moment release. Long‐period phases such as the W ‐phase and surface waves that better characterize total moment release can also be incorporated in the processing.

In industrial facilities sites, the conventional method determining the earthquake magnitude (M) using earthquake ground-motion records is generally not applicable due to the poor quality of data. Therefore, a new methodology is proposed for determining the earthquake magnitude in real-time based on the amplitude measures of the ground-motion acceleration mostly from S-wave packets with the higher signal-to-ratios, given the Vs30 of the site. The amplitude measures include the bracketed cumulative parameters and peak ground acceleration (As). The cumulative parameter is either CAV (Cumulative Absolute Velocity) with 100 SPS (sampling per second) or BSPGA (Bracketed Summation of the PGAs) with 1 SPS. The arithmetic equations to determine the earthquake magnitude are derived from the CAV(BSPGA)-As-M relations. For the application to broad ranges of earthquake magnitude and distance, the multiple relations of CAV(BSPGA)-As-M are derived based on worldwide earthquake records and successfully used to determine the earthquake magnitude with a standard deviation of ±0.6M.

Attempts have been made to investigate the relationships between various earthquake magnitude scales for the region of the Gulf of Guinea, namely moment magnitude (Mw), surface wave magnitude (Ms), body wave magnitude (mb) and local magnitude (ML). The study involves a sum of 535 earthquake data from the period of 1918 to 2016. It was found that M s − M w ; M w − M L and m b − M w scales are in fairly good agreement while m b − M s magnitude scale differs by a magnitude unit of 1.45. Since the region of study is seismically active and mainly under the ocean, comprising of the mid-Atlantic ridges and the plate boundary, the seismo-tectonics of the study region is inferred from the obtained Gutenberg-Richter (GR) recurrence parameters. The inferences made are the prime input to the seismic hazard assessment of the region.

[1] We examine five different methods to estimate an earthquake's magnitude using only P wave data for use in earthquake early warning systems. We test two input parameters: the maximum predominant period of the P wave (τpmax) and the displacement amplitude of the P wave's vertical component (Pd). We apply our algorithms to 174 earthquakes 3.0

This study investigates whether real-time strong ground motion data from seismic stations could have been used to provide an accurate estimate of the magnitude of the 2011 Tohoku-Oki earthquake in Japan. Ultimately, such an estimate could be used as input data for a tsunami forecast and would lead to more robust earthquake and tsunami early warning. We collected the strong motion accelerograms recorded by borehole and free-field (surface) Kiban Kyoshin network stations that registered this mega-thrust earthquake in order to perform an off-line test to estimate the magnitude based on ground motion prediction equations (GMPEs). GMPEs for peak ground acceleration and peak ground velocity (PGV) from a previous study by Eshaghi et al. in the Bulletin of the Seismological Society of America 103. (2013) derived using events with moment magnitude (M) ≥ 5.0, 1998–2010, were used to estimate the magnitude of this event. We developed new GMPEs using a more complete database (1998–2011), which added only 1 year but approximately twice as much data to the initial catalog (including important large events), to improve the determination of attenuation parameters and magnitude scaling. These new GMPEs were used to estimate the magnitude of the Tohoku-Oki event. The estimates obtained were compared with real time magnitude estimates provided by the existing earthquake early warning system in Japan. Unlike the current operational magnitude estimation methods, our method did not saturate and can provide robust estimates of moment magnitude within ~100 s after earthquake onset for both catalogs. It was found that correcting for average shear-wave velocity in the uppermost 30 m ( $$ V_{{{\text{s}}_{30} }} $$ ) improved the accuracy of magnitude estimates from surface recordings, particularly for magnitude estimates of PGV (Mpgv). The new GMPEs also were used to estimate the magnitude of all earthquakes in the new catalog with at least 20 records. Results show that the magnitude estimate from PGV values using borehole recordings had the smallest standard deviation among the estimated magnitudes and produced more stable and robust magnitude estimates. This suggests that incorporating borehole strong ground-motion records immediately available after the occurrence of large earthquakes can provide robust and accurate magnitude estimation.

[1] The combination of GPS and strong-motion data to estimate seismogeodetic waveforms creates a data set that is sensitive to the entire spectrum of ground displacement and the full extent of coseismic slip. In this study we derive earthquake magnitude scaling relationships using seismogeodetic observations of either P wave amplitude or peak ground displacements from five earthquakes in Japan and California ranging in magnitude from 5.3 to 9.0. The addition of the low-frequency component allows rapid distinction of earthquake size for large magnitude events with high precision, unlike accelerometer data that saturate for earthquakes greater than M 7 to 8, and is available well before the coseismic displacements are emplaced. These results, though based on a limited seismogeodetic data set, support earlier studies that propose it may be possible to estimate the final magnitude of an earthquake well before the rupture is complete.

On 8 September 2017, a great (M_w 8.2) normal faulting earthquake ruptured within the subducting Cocos Plate ~70 km landward from the Middle American Trench beneath the Tehuantepec gap. Iterative inversion and modeling of teleseismic and tsunami data and prediction of GPS displacements indicate that the steeply dipping rupture extended ~180 km to the northwest along strike toward the Oaxaca coast and from ~30 to 70 km in depth, with peak slip of ~13 m. The rupture likely broke through the entire lithosphere of the young subducted slab in response to downdip slab pull. The plate boundary region between the trench and the fault intersection with the megathrust appears to be frictionally coupled, influencing location of the detachment. Comparisons of the broadband body wave magnitude (m_B) and moment-scaled radiated energy (E_R/M_0) establish that intraslab earthquakes tend to be more energetic than interplate events, accounting for strong ground shaking observed for the 2017 event.

We obtained a robust regional body-wave magnitude scale mb(Pn) for earthquakes along the Northern mid-Atlantic Ridge by using Pn wave recorded at continental stations. The new magnitude scale is mb(Pn) = log10 A [nm] - 1.86 log10 (100/∆) [km] + C + 1.62, where A is the zero-to-peak amplitude of Pn wave on the simulated vertical Wood-Anderson seismogram in nanometers, ∆ is the epicentral distance in kilometers, 1.86 represents amplitude attenuation, C is the station correction, and 1.62 anchors the mb(Pn) to the moment magnitude (MW), plus amplitude loss in the two crustal legs. By using moment magnitude as reference, we obtained the event magnitude adjustments (EMA), which represent the difference between the known long-period MW and the short-period mb(Pn). EMAs correlate with the source property, where ridge events show strong long-period waves but poor high-frequency signals which lead to mb(Pn) MW and negative adjustment of -0.20±0.24 m.u. Almost all normal faulting events are along spreading ridges, whereas strike-slip events are along the fracture zones and transform faults, hence, we developed source specific magnitude adjustments (SSMA), which range from +0.27 m.u. for earthquakes along the ridges, to –0.26 m.u. for earthquakes along the transform faults. Using SSMA, we obtained a regional Pn magnitude that is consistent with MW and mb(P). The regression relationship is MW = 0.91 mb(Pn)[SSMA] + 0.46 with a standard deviation of ±0.15 m.u.

Run-up of long wave on a beach consisting of three pieces of constant but different slopes is studied. Linear shallow-water theory is used for incoming impulse evolution and non-linear corrections are obtained for the run-up stage. It is demonstrated that bottom profile influences the run-up characteristics and can lead to the resonance effects: increasing of wave height, particle velocity, and number of oscillations. Simple parameterization of tsunami source through an earthquake magnitude is used to calculate the run-up height versus earthquake magnitude. It is shown that resonance effects lead to the sufficient increasing of run-up heights for weakest earthquakes and tsunami wave does not break on chosen bottom relief if the earthquake magnitude does not exceed 7.8.

In this article, the seismic records of Japan’s Kik-net are selected to measure the acceleration, displacement, and effective peak acceleration of each seismic record within a certain time after P wave, then a continuous estimation is given on earthquake early warning magnitude through statistical analysis method, and Wenchuan earthquake record is utilized to check the method. The results show that the reliability of earthquake early warning magnitude continuously increases with the increase of the seismic information, the biggest residual happens if the acceleration is adopted to fit earthquake magnitude, which may be caused by rich high-frequency components and large dispersion of peak value in acceleration record, the influence caused by the high-frequency components can be effectively reduced if the effective peak acceleration and peak displacement is adopted, it is estimated that the dispersion of earthquake magnitude obviously reduces, but it is easy for peak displacement to be affected by long-period drifting. In various components, the residual enlargement phenomenon at vertical direction is almost unobvious, thus it is recommended in this article that the effective peak acceleration at vertical direction is preferred to estimate earthquake early warning magnitude. Through adopting Wenchuan strong earthquake record to check the method mentioned in this article, it is found that this method can be used to quickly, stably, and accurately estimate the early warning magnitude of this earthquake, which shows that this method is completely applicable for earthquake early warning.

Seismic behaviors of long-span connected structures under multi-dimensional and earthquake excitation while considering wave passage effect are investigated through both numerical simulation and a shaking table test on a scaled model. It is found that seismic responses will be increased significantly if multi-dimensional earthquake excitation is considered; and wave-passage effect has diverse influence on different elements. Also special attentions should be paid to those elements near connections between the main tower and the corridor which inertial forces may change a lot when subjected to Traveling wave excitation with different apparent velocities. Moreover, the vertical acceleration responses of the corridor can be increased significantly due to wave passage effect. Therefore, it is necessary for aseismic design of long-span connected structure to take into account multi-dimensional earthquake components and multi-support earthquake excitations with different apparent velocities.

The rapid determination of its magnitude soon after a great earthquake is necessary for the issuing of effective tsunami warnings, as demonstrated in the great earthquake off Tohoku district in Japan on March 11, 2011. The earthquake magnitude for the first tsunami warning was underestimated due to magnitude saturation. This paper proposes a method to determine magnitude rapidly from peak velocity and displacement of long-period seismic waves up to 100 seconds at local stations. When waveform data at local stations are available, the magnitude from S-wave peaks is expected to be determined faster than that from only P-wave peaks. It takes about 140 seconds to estimate a magnitude of about 9 for the March 11, 2011, earthquake, which would enable us to issue the first tsunami warning within three minutes after the same type of earthquake.

[1] We explore the application of GPS data to earthquake early warning and investigate whether the coseismic ground deformation can be used to provide fast and reliable magnitude estimations and ground shaking predictions. We use an algorithm to extract the permanent static offset fromGPS displacement time series and invert for theslip distribution on the fault plane, which is discretized into a small number of rectangular patches. We developed a completely “self-adapting” strategy in which the initial fault plane model is built based on a quick, approximate magnitude estimation and is then allowed to increase in size based on the evolutionary magnitude estimation resulting from the slip inversion. Two main early warning outputs are delivered in real-time: magnitude and the along-strike extent of the rupture area. These are finally used to predict the expected ground shaking due to the finite source. We tested the proposed strategy by simulating real-time environments for three earthquakes. For theMw9.0, 2011 Tohoku-Oki earthquake, our algorithm provides the first magnitude estimate of 8.2 at 39 s after the origin time and then gradually increases to 8.9 at 120 s. The estimated rupture length remains constant from the outset at ~360 km. For the Mw 8.3, 2003 Tokachi-Oki earthquake, the initial magnitude estimate is 8.5 at 24 s and drops to 8.2 at 40 s with a rupture length of 290 km. Finally, for the Mw 7.2, 2010 El Mayor-Cucapah earthquake, the magnitude estimate is 7.0 from the outset with a rupture length of 140 km. The accuracy of the ground shaking prediction using the GPS-based magnitude and finite extent is significantly better than existing seismology-based point source approaches. This approach would also facilitate more rapid tsunami warnings.

There exist various types of the WEC (Wave Energy Converter), and among them, the point absorber is the most popularly investigated type. However, it is difficult to find examples of systematically measured data analysis for the design of the point absorber type of power buoy in the world. The study investigates the wave load acting on the point absorber type resonance power buoy wave energy extraction system proposed by Kweon et al. (2010). This study analyzes the time series spectra with respect to the three-year wave data (2002.05.01~2005.03.29) measured using the pressure type wave gage at the seaside of north breakwater of Hupo harbor located in the east coast of the Korean peninsula. From the analysis results, it could be deduced that monthly wave period and wave height variations were apparent and that monthly wave powers were unevenly distributed annually. The average wave steepness of the usual wave was 0.01, lower than that of the wind wave range of 0.02-0.04. The mode of the average wave period has the value of 5.31 sec, while mode of the wave height of the applicable period has the value of 0.29 m. The occurrence probability of the peak period is a bi-modal type, with a mode value between 4.47 sec and 6.78 sec. The design wave period can be selected from the above four values of 0.01, 5.31, 4.47, 6.78. About 95% of measured wave heights are below 1 m. Through this study, it was found that a resonance power buoy system is necessary in coastal areas with low wave energy and that the optimal design for overcoming the uneven monthly distribution of wave power is a major task in the development of a WEF (Wave Energy Farm). Finding it impossible to express the average spectrum of the usual wave in terms of the standard spectrum equation, this study proposes a new spectrum equation with three parameters, with which basic data for the prediction of the power production using wave power buoy and the fatigue analysis of the system can be given.

− In this paper time series wave data are simulated using wave spectrum with random phases of thewave signal. The simulated wave signals are used to study the effect of the sampling rate on the ocean wavecharacteristics. Effect of sampling rate on wave data which include extreme wave such as freak waves areexamined and various wave characteristics including abnormality index (AI), kurtosis of wave profile and maxi-mum wave height are examined. Various wave heights are decreased as the sampling rate decreases. The zero-thmoment of the wave spectrum does not affect much on the sampling rate but the second moment are greatelyaffected on the sampling rate. The error due to the sampling rate is decreases as the wave period increases. Theerror in significant wave height based on the wave spectrum H s is smaller than that on the time domain methodH 1/3 . AI index and kurtosis of wave profile do not deviate much from the exact date as long as the sampling rateis greater than 1 Hz. Ocean wave measurement with the sampling frequency higher than 1 Hz will result theerror less than 5% in estimating the height of extreme waves.Keywords: Ocean Wave statistics(해양파 통계특성), Sampling rate(샘플링 레이트), Extreme wave height(극한파고), Freak wave(이상파랑)

Richter gave an empirical relation between surface wave (Rayleigh Waves) magnitude , Ms, and body wave magnitude, mb, ( generally short P type body waves of period 1 sec). At the outset, we have tried to modify the Richter's relation by taking into account of the earthquake data of the North-East India and its adjoining region. Then we analyse the applicability of surface wave magnitude scale and body wave magnitude scale for the seismicity study of the region. Lastly the completeness of the earthquake datafile is checked. Various statistical methods are adopted in this present study. It has been seen that there is not much difference between the values of surface wave magnitude obtained from Richter's relation and modified Richter's relation. Since error is less,it would be better if modified Richter's relation is applied. From the study of applicability it is found that error is less if body wave magnitude is taken in the seismicity study. From the completeness analysis of the datafile it has been found that the datafile is complete from different period onwards for different magnitudes.

The critical technology of Earthquake Early Warning (EEW) is determining the size of an earthquake and the predicted ground motion at given site, from the first few seconds of the P wave arrivals. Currently, there were two different approaches to the EEW magnitude estimation, the predominant period method and the peak amplitude method. However, both methods mentioned above had some disadvantages, such as significant uncertainty and saturation at great magnitude. To improve the results of magnitude estimation, a combined method using predominant period τc and peak amplitude of acceleration Pmax was introduced. Compared with the predominant period method and the peak amplitude method, the estimation standard deviation level of the combined method is 0.42 using NSMP strong motion data. The magnitude estimation results of the first three seconds P wave indicate that, the estimation precision of combined method is higher than those of the two methods, the predominant period method and the peak amplitude method, and the saturation at great magnitude is improved.

Heterodyne laser interferometer, which is used as a sensor for high-precision displacement measurement, is used to measure the ground motion and seismic waves as a seismometer. Through the displacement variation obtained by the precision measurement, we predict the magnitude of the earthquake. The Recursive Least Square (RLS) method reduces the error of earthquake magnitude prediction. RLS method is to update the relation between the magnitude and P d adaptively to predict the magnitude of earthquake more accurately. With the simulation results, we reduced error factors and improved the accuracy of earthquake magnitude estimation.

Wave is a general term given to ‘disturbance in water’. The waves produce humungous amounts of energy and therefore the study of different characteristics associated with waves becomes an important aspect. One such characteristic is the wave height. The height of a wave determines the impact that it would have when it hits the surface thereby playing a crucial role in deciding the quality and commercial viability of a beach and in determining the extent of transportation of sediments to proximate coastal areas. If the wave becomes very vigorous then it would pose a serious threat to the lives of the people inhabiting coastal areas. Therefore the analysis of different characteristics of waves becomes all the more important. In this paper, we have presented a statistical estimation of one such characteristic namely the wave height, which is also one of the most significant parameters used for estimating wave energy. In our review, we have used fundamental distribution functions to model the wave height, and have calculated error using various error detection tests thereby concluding the best fit for wave height. We have also provided a retrospective view of wave energy potential, in the light of significant wave height analyzed.

In this paper, a new vertical broadband seismometer is designed, simulated, and evaluated. The proposed seismometer has a bandwidth from 40 s to 50 Hz and sensitivity to ground velocity of 1500 V’/m/s. The mechanical suspension used in the proposed design is a mass-leaf spring rotational pendulum. The displacement of the seismic mass is sensed by a laser interferometer and then forwarded to an electronic force feedback system which feeds a linear actuator to keep the mass almost fixed in its position. The current needed to fix the mass in its position is an indication of the ground acceleration. The performance of the simulated seismometer is evaluated by applying a data record of two actual earthquakes to the simulated model and comparing its response to the earthquakes with that of a real seismometer (Trillium-40) having the same bandwidth and sensitivity. The proposed seismometer has performed within 0.4 % residual variance for the local event and 0.03 % residual variance for the regional one compared to Trillium-40.

Our knowledge of the absolute S wave velocities of the oceanic lithosphere is mainly based on global surface wave tomography, local active seismic or compliance measurements using oceanic infragravity waves. The results of tomography give a rather smooth picture of the actual S wave velocity structure and local measurements have limitations regarding the range of elastic parameters or the geometry of the measurement. Here, we use the P wave polarization (apparent P wave incidence angle) of teleseismic events to investigate the S wave velocity structure of the oceanic crust and the upper tens of kilometres of the mantle beneath single stations. In this study, we present an up to our knowledge new relation of the apparent P wave incidence angle at the ocean bottom dependent on the half space S wave velocity. We analyse the angle in different period ranges at ocean bottom stations (OBS) to derive apparent S wave velocity profiles. These profiles are dependent on the S wave velocity as well as on the thickness of the layers in the subsurface. Consequently, their interpretation results in a set of equally valid models. We analyse the apparent P wave incidence angles of an OBS data set which was collected in the Eastern Mid Atlantic. We are able to determine reasonable S wave velocity-depth models by a three step quantitative modelling after a manual data quality control, although layer resonance sometimes influences the estimated apparent S wave velocities. The apparent S wave velocity profiles are well explained by an oceanic PREM model in which the upper part is replaced by four layers consisting of a water column, a sediment, a crust and a layer representing the uppermost mantle. The obtained sediment has a thickness between 0.3 km and 0.9 km with S wave velocities between 0.7 km s−1 and 1.4 km s−1. The estimated total crustal thickness varies between 4 km and 10 km with S wave velocities between 3.5 km s−1 and 4.3 km s−1. We find a slight increase of the total crustal thickness from ∼5 km to ∼8 km towards the South in the direction of a major plate boundary, the Gloria Fault. The observed crustal thickening can be related with the known dominant compression in the vicinity of the fault. Furthermore, the resulting mantle S wave velocities decrease from values around 5.5 km s−1 to 4.5 km s−1 towards the fault. This decrease is probably caused by serpentinization and indicates that the oceanic transform fault affects a broad region in the uppermost mantle. Conclusively, the presented method is useful for the estimation of the local S wave velocity structure beneath ocean bottom seismic stations. It is easy to implement and consists of two main steps: (1) measurement of apparent P wave incidence angles in different period ranges for real and synthetic data, and (2) comparison of the determined apparent S wave velocities for real and synthetic data to estimate S wave velocity-depth models.