Station Corrections Research Articles

An improved 1-D crustal velocity model for the Central Alborz (Iran) using Particle Swarm Optimization algorithm

Summary We present an improved 1-D velocity model of the crust in the Central Alborz region using one of the powerful methods in global optimization techniques named Fuzzy Self-Tuning Particle Swarm Optimization (hereafter called FST-PSO). The FST-PSO generates random particles (velocity models) in a pre-defined solution space in which after number of iterations they lead to a model that yields best fits to the data. The ability of using any error statistics equally leads the algorithm to be independent of the velocity model form. As the PSO family members use only random processes to generate new models, they are inherently stable and avoid all numerical problems encountered in deterministic methods due to matrix inversion. Taking advantage of fuzzy logics implemented in FST-PSO, no parameters are needed to be adjusted including social, cognitive and inertia for running the program and can be used “out-of-the-box”. The proficiency of this method first is checked on both synthetic and real datasets. Then it is applied on a unique large amount of local earthquakes to calculated 1-D velocity model of the central Alborz, Iran. Relocation of events using our new velocity model and station corrections results to considerable reduction in RMS, horizontal and depth errors which obviously lead to a more precise events catalog. The spatial distribution of station corrections correlates well geological features. The positive delays in this area are consistent with Pliocene to Quaternary sedimentary cover spread in different parts of the study area, while the negative delays indicating on high velocity anomaly beneath the station are observed on hard Igneous rocks mainly around the Mosha fault. Positive delays of few stations located on hard bed rocks can be related to the shallow magma chamber of the Damavand volcano. Updating the seismicity map using this catalog, reveals a good correlation between existing active faults trends like Mosha, Khazar, North Alborz, Garmsar, and Taleghan and well-located earthquakes.

Development of local magnitude scale for the Northern Punjab, Pakistan

We developed a local magnitude scale for the Northern Punjab (Potwar Plateau and Salt Range), using seismic data of CES (Centre for Earthquake Studies). The region is tectonically stable, but surrounded by active geological structures (i.e., Main Boundary Thrust, Sulaiman Range, and Jhelum Fault). The imparted stresses adjust both seismically (moderate to small magnitude earthquakes) and aseismically in decollement. Previously, Southern California magnitude scale was being used to determine local magnitude for compilation of seismic catalog. Difference in geology and tectonics between Southern California and Northern Punjab may lead to systematic errors in hazard assessment based on this catalog. To address this problem, we selected 231 seismic events for a period of 07 years with ML 2.0 and above, that correspond to 2800 records on 21 seismic stations. We chose data of seismic events with hypocentral distance less than 600 km and recorded on five stations at least. We then inverted the synthetic Wood-Anderson amplitudes of selected data for station and distance corrections. Accordingly, the new magnitude scale for Northern Punjab is given by the following: ML = logA + 0.869log(r) + 0.00115(r) − 1.53, where A is the amplitude in nanometers on synthetic Wood-Anderson seismograph and r is the hypocentral distance in kilometers. We observed lower attenuation of seismic waves in our study area as compared to Southern California. Lower standard deviation (i.e., reduction in variance to 45.4% ) in magnitude residuals shows that there is less deviation for newly developed scale as compared to that of Southern California scale. Values of station correction factors for different stations of local network vary between − 0.5 to + 0.5, which suggest variation in station site effects.

Modeling of maintenance systems for railway infrastructure facilities based on the theory of mass service

The article is substantiated the necessity of intro-and dynamics of change are proposed to be implemented within ducing the mechanism of predictable maintenance of railway trans-the framework of a specially created decision support system. It port infrastructure into the practice of the transportation process. was also proposed to use the mathematical apparatus of queuing The functions of object monitoring, diagnostics of their condition theory to implement the tasks of analyzing and synthesizing the structure and functions of the system for organizing maintenance of transport infrastructure facilities. Within the framework of this tool, a mathematical model for the synthesis of maintenance systems for railway infrastructure facilities was constructed and analyzed, and a network of queuing systems describing monitoring, diagnostics and maintenance of these facilities was considered. The analysis technique of the infrastructure objects includes the procedure for structuring the railway transport object in the form of a combination of queuing systems and queuing networks, analysis of their parameters, analysis and optimization of information flows in queuing networks. The features of the application of the developed model for the solution of three practical problems are analyzed: technical and commercial inspection of trains at the sorting station reception, identification and correction of wheelset defects on thermal anomalies, development of a system for diagnosing the negative dynamics of freight cars. A model is described that allows calculating the main parameters (service intensity, service time and location in network) for a network that includes the source of applications (the transportation process), the diagnostic subsystems (as part of the decision support system - DSS) and the maintenance depoes.

Calculating the Station Corrections to Earthquake Energy Class and the Acoustic Impedance for Kamchatka Stations

This paper describes a method for calculating the station corrections to earthquake energy class and the acoustic impedance based on records of earthquake codas in the 0.8–1.8 Hz frequency band. The calculation is based on measurements of the relative coda level at two stations, with one of the two being used as the reference. The data were recorded by digital seismometers: CMG-3TB (GURALP), CMG-5TD (GURALP), CMG-6TD (GURALP), and GMS-AC-73i HHV (GeoSIG). We present estimates of class corrections for the Kamchatka network of seismic stations.

Response of Gravity, Magnetic, and Geoelectrical Resistivity Methods on Ngeni Southern Blitar Mineralization Zone

The research with entitle response of gravity, magnetic, and geoelectrical resistivity methods on Ngeni Southern Blitar mineralization zone has been done. This study aims to find the response of several geophysical methods of gravity, magnetic, and geoelectrical resistivity in an integrated manner. Gravity data acquisition was acquired 224 data which covers the whole region of Blitar district by using Gravity Meter La Coste & Romberg Model “G”, and magnetic data acquisition were acquired 195 data which covers the southern Blitar district only by using Proton Precession Magnetometer G-856. Meanwhile geoelectrical resistivity data only done in Ngeni village which is the location of phyropilite mining with the composition content of Fe, Si, Ca, S, Cu, and Mn by using ABEM Terrameter SAS 300C. Gravity data processing was performed to obtain the Bouguer anomaly value, which included unit conversion, tidal correction, drift correction, correction of tie point, base station correction, free air correction, and Bouguer correction. Magnetic data processing has been done by some corrections i.e daily, drift, and IGRF(International Geomagnetic Refference Field) to obtain the total magnetic anomaly. From gravity data processing has been obtained the simple Bouguer anomaly value in range from -10mGal until 115mGal. From this data processing has been obtained the total magnetic anomaly value in range from -650nT until 800nT. Meanwhile from geoelectrical resistivity 3.03Ωm until 11249.91 Ωm. There is a correlation between gravity anomaly, magnetic anomaly, and geoelectrical resistivity anomaly that are associated with deep anomaly, middle anomaly, and shallow anomaly.

On the link between stress field and small-scale hydraulic fracture growth in anisotropic rock derived from microseismicity

Abstract. To characterize the stress field at the Grimsel Test Site (GTS) underground rock laboratory, a series of hydrofracturing and overcoring tests were performed. Hydrofracturing was accompanied by seismic monitoring using a network of highly sensitive piezosensors and accelerometers that were able to record small seismic events associated with metre-sized fractures. Due to potential discrepancies between the hydrofracture orientation and stress field estimates from overcoring, it was essential to obtain high-precision hypocentre locations that reliably illuminate fracture growth. Absolute locations were improved using a transverse isotropic P-wave velocity model and by applying joint hypocentre determination that allowed for the computation of station corrections. We further exploited the high degree of waveform similarity of events by applying cluster analysis and relative relocation. Resulting clouds of absolute and relative located seismicity showed a consistent east–west strike and 70° dip for all hydrofractures. The fracture growth direction from microseismicity is consistent with the principal stress orientations from the overcoring stress tests, provided that an anisotropic elastic model for the rock mass is used in the data inversions. The σ1 stress is significantly larger than the other two principal stresses and has a reasonably well-defined orientation that is subparallel to the fracture plane; σ2 and σ3 are almost equal in magnitude and thus lie on a circle defined by the standard errors of the solutions. The poles of the microseismicity planes also lie on this circle towards the north. Analysis of P-wave polarizations suggested double-couple focal mechanisms with both thrust and normal faulting mechanisms present, whereas strike-slip and thrust mechanisms would be expected from the overcoring-derived stress solution. The reasons for these discrepancies can be explained by pressure leak-off, but possibly may also involve stress field rotation around the propagating hydrofracture. Our study demonstrates that microseismicity monitoring along with high-resolution event locations provides valuable information for interpreting stress characterization measurements.

Fórmulas de magnitud local para la zona del paletará (cauca, colombia)

The determination of the local magnitude scale (ML) for the Paletara zone (PZ), Colombia was performed for the first time by the inversion of the horizontal components of 2848 amplitudes at 18 seismic stations for VT and local tectonic earthquakes with focal depths less than 37 km and focal distances less than 220 km. The distance corrected function found in this study is −log(Ao) = 1,3541 log(r/17) + 0,001639(r − 17) + 2, where –log(Ao) is the empirically determined distance correction and r is the hypocentral distance. Accordingly, the local magnitude scale for PZ is defined as: ML = log(Amm) + 1,3541 log(r/17) + 0,001639(r − 17) 2 + S, or according to IASPEI formulation: ML = log(Anm) + 1,3541 log(r) + 0,001639r − 2,37 + S where Amm is the peak amplitude in mm simulated in a Wood-Anderson seismogram, Anm is the peak amplitude in nm simulated in a Wood-Anderson seismogram, with a magnification of 1, and S is the station correction due to differences in site amplification.

Earthquake Magnitude Relationships for the Saint Peter and Saint Paul Archipelago, Equatorial Atlantic

We have investigated several relationships between ML, M(NEIC) and Mw for the earthquakes locally recorded in the Saint Peter and Saint Paul Archipelago (SPSPA), Equatorial Atlantic. Because we only have one station in the area, we could not derive attenuation relations for events recorded at different distances at different stations. Our approach was then to compare our ML estimates with magnitudes reported by NEIC. This approach produced acceptable results particularly for epicentral distance smaller than 100 km. For distances greater that 100 km, there is a systematic increase in the residuals probable due to the lack of station correction and our inability to accurately estimate Q. We also investigate the Mw—M(NEIC) relationship. We find that Mw estimates using S-wave produce smaller residuals when compared with both M(NEIC). Finally, we also investigate the ML—Mw relationship and observe that given the data set we have, the 1:1 holds. We believe that the use of the present methodologies provide consistent magnitude estimates between all the magnitudes investigated that could be used to better assess seismic hazard in the region.

Regional Pn Body‐Wave Magnitude Scale mb(Pn) for Earthquakes Along the Northern Mid‐Atlantic Ridge

AbstractWe 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/Δ) [km] + C + 1.62, where A is the zero‐to‐peak amplitude of Pn wave on the simulated vertical Wood‐Anderson seismogram in nanometers, Δ 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 (EMAs), 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 that lead to mb(Pn) < Mw and positive EMA of +0.08 ± 0.26 magnitude units (m.u.), whereas transform fault earthquakes show relatively strong high‐frequency waves that 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 (SSMAs), 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.

Crustal Structure in the Western Part of Romania from Local Seismic Tomography

The inner part of the Carpathians in Romania belongs to the Carpathians-Pannonian system bordered by the Eastern Carpathians to the north and east, Southern Carpathians to the south and Pannonian Basin to the west. It is a complex tectonic region with differential folding mechanisms, post-collisional kinematics, rheology and thermal properties, including within its area the Apuseni Mountains and the Transylvanian Basin. The purpose of this study is to map the 3-D structure of the crust over this region on the basis of local earthquake data. Input data were recorded during the South Carpathian Project (2009–2011), a successful collaboration between the Institute of Geophysics and Tectonics of the University of Leeds and the National Institute for Earth Physics (NIEP), Romania. A temporary array of 32 broadband seismic stations (10 CMG-40T, 8 CMG-3T and 14 CMG-6TD) was installed across the western part of Romania (spaced at 40 to 50 km intervals) during the project. In addition, 25 stations deployed in the eastern Hungary and Serbia was considered. P- and S-wave arrivals are identified for all the selected events (minimum 7 phases per event with reasonable signal/noise ratio). All the events are first relocated using Joint Hypocentre Determination (JHD) technique. Then the well-located events were inverted to determine the crustal structure using LOTOS algorithm. The lateral variations of the crustal properties as resulted from the tomography image are interpreted in correlation with the station corrections estimated by JHD algorithm and with the post-collisional evolution of the Carpathians-Pannonian system.

Local magnitude scale for Valle Medio del Magdalena region, Colombia

A local Magnitude (ML) scale for Valle Medio del Magdalena (VMM) region was defined by using 514 high quality earthquakes located at VMM area and inversion of 2797 amplitude values of horizontal components of 17 stations seismic broad band stations, simulated in a Wood-Anderson seismograph. The derived local magnitude scale for VMM region was: ML=log(A)+1.3744∗log(r)+0.0014776∗r−2.397+SWhere A is the zero-to-peak amplitude in nm in horizontal components, r is the hypocentral distance in km, and S is the station correction. Higher values of ML were obtained for VMM region compared with those obtained with the current formula used for ML determination, and with California formula.With this new scale ML values are adjusted to local conditions beneath VMM region leading to more realistic ML values. Moreover, with this new ML scale the seismicity caused by tectonic or fracking activity at VMM region can be monitored more accurately.

Locating seismicity on the Arctic plate boundary using multiple-event techniques and empirical signal processing

The oceanic boundary separating the Eurasian and North American plates between 70 and 84 degrees North hosts large earthquakes which are well recorded teleseismically, and many more seismic events at far lower magnitudes that are well recorded only at regional distances. Existing seismic bulletins have considerable spread and bias resulting from limited station coverage and deficiencies in the velocity models applied. This is particularly acute for the lower magnitude events which may only be constrained by a small number of Pn and Sn arrivals. Over the past two decades there has been a significant improvement in the seismic network in the Arctic: a difficult region to instrument due to the harsh climate, a sparsity of accessible sites (particularly at significant distances from the sea), and the expense and difficult logistics of deploying and maintaining stations. New deployments and upgrades to stations on Greenland, Svalbard, Jan Mayen, Hopen, and Bjornoya have resulted in a sparse but stable regional seismic network which results in events down to magnitudes below 3 generating high quality Pn and Sn signals on multiple stations. A catalog of several hundred events in the region since 1998 has been generated using many new phase readings on stations on both sides of the spreading ridge in addition to teleseismic P phases. A Bayesian multiple event relocation has resulted in a significant reduction in the spread of hypocenter estimates for both large and small events. Whereas single event location algorithms minimize vectors of time residuals on an event-by-event basis, the Bayesloc program finds a joint probability distribution of origins, hypocenters, and corrections to travel time predictions for large numbers of events. The solutions obtained favour those event hypotheses resulting in time residuals which are most consistent over a given source region. The relocations have been performed with different 1-D velocity models applicable to the Arctic region and hypocenters obtained using Bayesloc have been shown to be relatively insensitive to the specified velocity structure in the crust and upper mantle, even for events only constrained by regional phases. The patterns of time residuals resulting from the multiple-event location procedure provide well-constrained time correction surfaces for single-event location estimates and are sufficiently stable to identify a number of picking errors and instrumental timing anomalies. This allows for subsequent quality control of the input data and further improvement in the location estimates. We use the relocated events to form narrowband empirical steering vectors for wavefronts arriving at the SPITS array on Svalbard for azimuth and apparent velocity estimation. We demonstrate that empirical matched field parameter estimation determined by source region is a viable supplement to planewave f-k analysis, mitigating bias and obviating the need for Slowness and Azimuth Station Corrections (SASCs). A database of reference events and phase arrivals is provided to facilitate further refinement of event locations and the construction of empirical signal detectors.

BARENTS16: a 1-D velocity model for the western Barents Sea

A minimum 1-D seismic velocity model for routine seismic event location purposes was determined for the area of the western Barents Sea, using a modified version of the VELEST code. The resulting model, BARENTS16, and corresponding station corrections were produced using data from stations at regional distances, the vast majority located in the periphery of the recorded seismic activity, due to the unfavorable land–sea distribution. Recorded seismicity is approached through the listings of a joint bulletin, resulting from the merging of several international and regional bulletins for the region, as well as additional parametric data from temporary deployments. We discuss the challenges posed by this extreme network-seismicity geometry in terms of velocity estimation resolution and result stability. Although the conditions do not facilitate the estimation of meaningful station corrections at the farthermost stations, and even well-resolved corrections do not have a convincing contribution, we show that the process can still converge to a stable velocity average for the crust and upper mantle, in good agreement with a priori information about the regional structure and geology, which reduces adequately errors in event location estimates.

Accurate relocation of seismicity along the North Aegean Trough and its relation to active tectonics

The tectonics of northern Aegean are affected by the westward push of Anatolia and the gravitational spreading of the Aegean lithosphere that promote transtensional deformation in the area. This regime is also responsible for the creation of a series of pull-apart basins, collectively known as the North Aegean Trough. This work accurately relocates a total of 2300 earthquakes that were recorded along the North Aegean Trough during 2011–2016 by stations of the Hellenic Unified Seismic Network (HUSN) and strong-motion sensors. Absolute locations for these events were obtained using a nonlinear probabilistic algorithm and utilizing a minimum 1D velocity model with station corrections. The hypocentral depth distribution of these events shows a peak at 8km diminishing gradually down to 20km. A systematic overestimation of hypocentral depths is observed in the routine locations provided by the National Observatory of Athens where the majority of events appear to be deeper than 15km. In order to obtain more accurate relative locations these events were relocated using the double-difference method. A total of 1693 events were finally relocated with horizontal and vertical uncertainties that do not exceed 0.11km and 0.22km respectively. Well-defined clusters of seismicity can be observed along the Saros and Sporades basins as well as the Kassandra and Sithonia peninsulas. These clusters either occur along the well-known NE-SW strike-slip faults bounding the basins, or along normal faults whose strike is perpendicular to the regional minimum stress axis. Locking depth along the North Aegean Trough is found to be remarkably stable between 13 and 17km. This is likely a consequence of simultaneous reduction along the SW direction of heat flow (from 89 to 51mW/m2) and strain rate (from 600 to 50nstrain/yr) whose opposite effects are canceled out, precluding any sharp changes in locking depth.

Development of nationwide amplification map of response spectrum for Japan based on station correction factors

In this study, the characteristics of site amplification at seismic observation stations in Japan were estimated using the attenuation relationship of each station´s response spectrum. Ground motion records observed after 32 earthquakes were employed to construct the attenuation relationship. The station correction factor at each KiK-net station was compared to the transfer functions between the base rock and the surface. For each station, the plot of the station correction factor versus the period was similar in shape to the graphs of the transfer function (amplitude ratio versus period). Therefore, the station correction factors are effective for evaluating site amplifications considering the period of ground shaking. In addition, the station correction factors were evaluated with respect to the average shear wave velocities using a geographic information system (GIS) dataset. Lastly, the site amplifications for specific periods were estimated throughout Japan.

Calibrating the amplitude source location (ASL) method by using active seismic sources: An example from Te Maari volcano, Tongariro National Park, New Zealand

AbstractA frequently applied amplitude source location (ASL) method is here calibrated and optimized by using active seismic sources located at the surface of a dry stream channel. The ASL produced location discrepancies larger than 1.0 km laterally and 500 m in depth by using independently determined velocity model, attenuation, and site amplification factors (AFs). Sensitivity tests for ASL input parameters show that attenuation and velocity have moderate influence on the location but are easy to independently constrain. AFs are shown to strongly influence the location, and their application may introduce substantial location uncertainties. Model uncertainties are accommodated with either lateral or depth changes depending on the input parameters, station corrections, and the source‐station geometry.

Calibration of the local magnitude scale (M L ) for Peru

We propose a local magnitude scale (M L ) for Peru, based on the original Richter definition, using 210 seismic events between 2011 and 2014, recorded by 35 broadband stations of the National Seismic Network operated by the Geophysical Institute of Peru. In the solution model, we considered 1057 traces of maximum amplitude records on the vertical channel from simulated Wood-Anderson seismograms of shallow events (depths between 0 and 60 km) and hypocentral distances less than 600 km. The attenuation factor has been evaluated in terms of geometrical spreading and anelastic attenuation coefficients. The magnitude M L was defined as M L = L o g 10 A W A +1.5855L o g 10(R/100)+0.0008(R−100)+3±S, where, A W A is the displacement amplitude in millimeters (Wood-Anderson), R is the hypocentral distance (km), and S is the station correction. The results obtained for M L have good correlation with the m b , M s and M w values reported the ISC and NEIC. The anelastic attenuation curve obtained has a similar behavior to that other highly seismic regions. Station corrections were determined for all stations during the regression analysis resulting in values ranging between −0.97 and +0.73, suggesting a strong influence of local site effects on amplitude.

Local Earthquake Magnitude Scale andb‐Value for the Danakil Region of Northern Afar

The Danakil region of northern Afar is an area of ongoing seismic and volcanic activity caused by the final stages of continental breakup. To improve the quantification of seismicity, we developed a calibrated local earthquake magnitude scale. The accurate calculation of earthquake magnitudes allows the estimation of b ‐values and maximum magnitudes, both of which are essential for seismic‐hazard analysis. Earthquake data collected between February 2011 and February 2013 on 11 three‐component broadband seismometers were analyzed. A total of 4275 earthquakes were recorded over hypocentral distances ranging from 0 to 400 km. A total of 32,904 zero‐to‐peak amplitude measurements ( A ) were measured on the seismometer’s horizontal components and were incorporated into a direct linear inversion that solved for all individual local earthquake magnitudes ( M L), 22 station correction factors ( C ), and 2 distance‐dependent factors ( n , K ) in the equation M L=log( A )−log( A )+ C . The resultant distance correction term is given by −log( A )=1.274336log( r /17)−0.000273( r −17)+2. This distance correction term suggests that attenuation in the upper and mid‐crust of northern Afar is relatively high, consistent with the presence of magmatic intrusions and partial melt. In contrast, attenuation in the lower crust and uppermost mantle is anomalously low, interpreted to be caused by a high melt fraction causing attenuation to occur outside the seismic frequency band. The calculated station corrections serve to reduce the M L residuals significantly but do not show a correlation with regional geology. The cumulative seismicity rate produces a b ‐value of 0.9±0.06, which is higher than most regions of continental rifting yet lower than values recorded at midocean ridges, further supporting the hypothesis that northern Afar is transitioning to seafloor spreading. [Electronic Supplement:][1] List of all local earthquakes used in the study with calculated local magnitudes and associated magnitude error. [1]: http://www.bssaonline.org/lookup/suppl/doi:10.1785/0120150253/-/DC1

Local magnitude estimation in Greece, based on recordings of the Hellenic Unified Seismic Network (HUSN).

A new relation is proposed for calculation of local magnitudes in Greece. For this purpose, there were used synthetic Wood-Anderson (SWA) recordings of 98 digital broad-band stations operating between 2007 and 2011. These stations are installed at the sites of the seismological networks of: a) the National Observatory of Athens(HL), b) the Department of Geophysics of the Aristotle University of Thessaloniki (HT), c) the Seismological Laboratory of the University of Athens (HA) and d) the Seismological Laboratory of the University of Patras (HP). All these institutions constitute the recently (2004) established Hellenic Unified Seismic Network (HUSN). These recordings are used to calculate a refined geometrical spreading factor and an anelastic attenuation coefficient, representative for Greece and surrounding area, proper for estimating local magnitudes in this region. Individual station corrections are also calculated in order to further ameliorate magnitude estimation accuracy. Comparison of such calculated local magnitudes with corresponding original moment magnitudes revealed that these two scales are equivalent for awide range of values (2.9≤MW≤6.4).

Magnitude M w in metropolitan France

The recent seismicity catalogue of metropolitan France Sismicite Instrumentale de l’Hexagone (SI-Hex) covers the period 1962–2009. It is the outcome of a multipartner project conducted between 2010 and 2013. In this catalogue, moment magnitudes (M w) are mainly determined from short-period velocimetric records, the same records as those used by the Laboratoire de Detection Geophysique (LDG) for issuing local magnitudes (M L) since 1962. Two distinct procedures are used, whether M L-LDG is larger or smaller than 4. For M L-LDG >4, M w is computed by fitting the coda-wave amplitude on the raw records. Station corrections and regional properties of coda-wave attenuation are taken into account in the computations. For M L-LDG ≤4, M w is converted from M L-LDG through linear regression rules. In the smallest magnitude range M L-LDG <3.1, special attention is paid to the non-unity slope of the relation between the local magnitudes and M w. All M w determined during the SI-Hex project is calibrated according to reference M w of recent events. As for some small events, no M L-LDG has been determined; local magnitudes issued by other French networks or LDG duration magnitude (M D) are first converted into M L-LDG before applying the conversion rules. This paper shows how the different sources of information and the different magnitude ranges are combined in order to determine an unbiased set of M w for the whole 38,027 events of the catalogue.