magnitude scale and quantification of earthquakes despite various shortcomings the earthquake magnitude scale is one of the most fundamental earthquake source parameters to be used for catalogs although use of a uniform scale is desirable it is not always possible because of changes in instrumentation the data reduction method and the magnitude formula the station distribution etc as a result various magnitude scales have been developed and are currently in use recent developments in seismometry and earthquake source theories provide more quantitative source parameters than the magnitude in order to maintain continuity and uniformity of the data it is important to relate these magnitude scales and the new parameters in view of this importance relations between different magnitude scales are examined with an emphasis on the difference in the period of the waves used for the magnitude determination use of several magnitude scales determined at different periods provides a convenient method for characterizing earthquakes the moment magnitude can be used to quantify both shallow and deep earthquakes on the basis of wave energy radiated and provides a uniform scheme

a new view of italian seismicity using 20 years of instrumental recordings in this paper we show the seismicity of the past 20 years that occurred in italy and surrounding regions hypocentral locations have been obtained by using p and s wave arrival times from the ingv national and several regional permanent seismic networks more than 48 000 events selected from an original data set of about 99 780 are used to reconstruct the most complete seismic picture of the italian region so far the seismicity distribution allows inference on seismotectonics of this complex region of subduction versus continental collision our results clearly reveal the geometry of the adria and the ionian subduction and a continuous normal fault belt in the upper crust following the apennines mountain range the depth of the seismogenic layer is computed from the cut off of seismicity at depth and shows large variations along and across the seismic active regions earthquakes are generated by the different velocity of slab retreat and the subsequent asthenospheric upwelling d 2004 elsevier b v all rights reserved

european mediterranean regional centroid moment tensors 1997 2000 the mediterranean region is seismically very active and undergoing rapid deformation earthquakes as strong as m 6 are present but relatively rare on the other hand moderate magnitude seismicity 4 5 m 5 5 is widespread and often damaging an improved knowedge of moderate magnitude earthquakes can contribute significantly to a better understanding of active tectonics in the region harvard centroid moment tensors cmt today represent the most widely used reference for reliable source mechanisms but modelling seismic sources with the cmt technique for earthquakes with magnitude less than m 5 5 5 is quite difficult since 1997 we are using an extension of the standard cmt algorithm to compute regional centroid moment tensors rcmt for moderate magnitude earthquakes mw as low as 4 0 analyzing intermediate period surface waves from regional and teleseismic seismograms we routinely apply the algorithm to european mediterranean seismicity to produce a catalog of seismic moment tensors for events with magnitude between 4 5 and 5 5 which generally are not included in the harvard cmt catalog in this paper we show the results for earthquakes that occurred between 1997 and 2000 consisting of 252 solutions and we discuss the characteristics of the catalog and the areas where these new data are most relevant

stress tensor orientation derived from fault plane solutions in the southwestern alps gephart and forsyth s method has been applied to estimate stress orientations from earthquake fault plane solutions of the southwestern alps a region where the tectonic stress regime is known to be fairly complex fault plane solutions have been either taken from the literature or computed using data from local and regional networks data refer to seismic events of magnitude in the range 2 5 5 3 which occurred in the last decades at depths between 0 and 25 km two zones with a different stress orientation have been identified in the studied area 44 0 45 5 n 6 5 8 5 e the western zone corresponding to the crest of the alpine belt where a high dip maximum compressive stress is found and the eastern zone alps chain to po plain transition characterized by an almost horizontal e w 1 and a nearly vertical 3 hypocenters of earthquakes used for stress inversion lie in the depth ranges 0 15 km and 5 25 km in the western and eastern zones respectively the transition between the two stress domains is very sharp and this is also indicated by space distribution of earthquake individual misfits to the respective stress models the findings of the present study are a good match for tectonic models which assume e w compression derived from the adria europe interaction and producing 1 major thrusting processes in the eastern side of the chain and 2 secondary tensional effects at very shallow depth beneath the alpine belt crest western zone of the area studied in this work

the relative motion between africa and eurasia as derived from itrf2000 and gps data 1 studies of intra and inter plate deformation typically need a model describing the motions of the stable part of the tectonic plates for reference purposes we have developed deos2k a model for the current motion of seven major tectonic plates derived from space geodetic observations this paper focuses on relative motion between africa and eurasia in the past this motion has been poorly established because of poor data coverage for africa deos2k is based on itrf2000 altamimi et al 2002 and new african gps observations it is an improvement over the nuvel 1a model for predicting the present day relative motions of these two plates deos2k predicts in northeastern africa that africa eurasia relative motion is about 40 smaller in magnitude than nuvel 1a and trends more to the northwest this is consistent with independent local geodetic observations a similar shift in orientation clockwise is observed at the western tip of the plate boundary

magnitude frequency relation for small earthquakes a clue to the origin of ƒmax of large earthquakes in order to test the hyothesis that the max of large earthquakes is due to the source effect and is causally related to the corner frequency of small earthquakes when it becomes constant below magnitude about 3 we constructed the frequency magnitude relation for earthquakes with magnitude range from 1 3 to 4 recorded at a borehole seismograph station operated by the university of southern california at baldwin hills in the middle of the newport inglewood fault a procedure was developed for an accurate estimation of moment magnitude from the measurement of coda amplitude as a function of lapse time the cumulative number of earthquakes per unit time period and area was estimated by finding the detection limit for ts p for each magnitude we found a clear depature of the observed log frequency magnitude relation for m 3 the observed frequency of earthquakes with m 0 5 is almost 10 times less than that expected from the extrapolation of empirical relation for earthquakes with magnitudes larger than 3 we conclude that the observed frequency magnitude relation departs from self similarity for earthquakes with magnitude smaller than about 3 this departure coincides with the widely observed departure of the moment corner frequency relation from self similarity these observations are consistent with the interpretation of max of large earthquakes in terms of the slip weakening instability model in which the critical slip may be a few tenths of a meter to a few meters and the cohesive zone size may be a few hundred meters to a few kilometers

widespread extension in the core of the western alps revealed by earthquake analysis the western alps are an active collision belt whose current stress field is inhomogeneous muller et al 1992 we report new seismological data which significantly improve our knowledge of this stress field about 1600 earthquakes which occurred in the western alps during the last 10 years were precisely located and 79 new focal solutions were computed the analysis of this database shows that widespread extension affects all the internal zones of the belt to better constrain the associated stress regime six stress tensors were computed using the gephart and forsyth 1984 method they show that the current tectonics of the western alps are contrasted with close variation in the stress regime transpression to the front of the belt contrasting with extension in the core of the belt the extensional direction is radial to the arcuate geometry of the belt and bounded outboard by the former thrust of the internal zones onto the external zone suggesting extensional reactivation of this inherited crustal discontinuity such widespread extension within the inner part of an actually ongoing collision belt cannot be explained by simple collision related tectonics we propose that intrabelt buoyancy forces such as those produced by a slab retreat or slab break off interfere with the boundary forces driven by the ongoing europe africa convergence

nonlinear frequency magnitude relationships for the hokkaido corner japan abstract frequency magnitude relationships are determined for a source region defined by a circular epicentral area of 50 km radius centered on the carnegie broadband seismograph at kmu in the southeast corner of hokkaido island japan within this region bounded by a maximum depth of 125 km more than 11 100 earthquakes were detected and cataloged by the hokkaido university network during the period july 1976 through january 1987 the seismicity is divided into two effectively decoupled suites crustal eurasian plate and subduction pacific plate the frequency magnitude recurrence distributions exhibit departures from linearity which are statistically significant below m d 2 5 for the crustal data suite and m d 3 5 for the subduction data suite three independent tests show the nonlinearity is not caused by incompleteness the catalog is complete down to magnitude 2 0 or less for both data suites these observations are therefore inconsistent with the linear gutenberg richter relationship which is assumed to be valid over any magnitude range for which the data are complete there are relatively more large events and fewer small events in the subduction suite the logarithm of the ratio of the number of crustal events to the number of subduction events versus magnitude is monotonically decreasing and remarkably linear over the magnitude range 1 0 to 5 0 this suggests that the observed nonlinearity of these two frequency magnitude relationships has a common origin

anisotropic loci in the mantle beneath central peru abstract seismic anisotropy of the upper mantle beneath the central part of peru is examined by analyzing shear waves observed at broad band stations and a temporary array of short period stations shear wave splitting is seen on various shear phases such as direct s waves from local intermediate to deep earthquakes scs waves from regional deep earthquakes and sks waves from teleseismic earthquakes it is inferred that the shear wave anisotropy in the uppermost 100 km of the subcontinental mantle overlying the subducted nazca plate is 0 5 at most while the anisotropy in the subslab asthenosphere depth range of about 150 350 km is 2 or greater the fast shear wave polarization direction in this depth range as observed at two broad band stations is 30 40 different from the absolute motion of the nazca plate this does not fit simple two dimensional 2 d models of olivine alignment caused by slab induced mantle flow and implies either the existence of a complex flow pattern in the asthenosphere underneath the nazca plate or the presence of an unknown mechanism for the anisotropy formation the lower mantle beneath central peru is found to be effectively isotropic for nearly vertically propagated shear waves

subduction of the nazca plate beneath peru as determined from seismic observations a detailed reinvestigation of seismicity in the southern half of peru using data from a local seismic network and a focal mechanism study using p wave first motions reveal that for the first 100 km of descent the slab as defined by this seismicity enters at a normal dip angle near 30 and that below this depth it is bent to a nearly horizontal angle this horizontal slab extends eastward for about 300 km and then dips steeply below the thick continental lithosphere scsp observations are found to be consistent with the profile of the subducting plate as determined from the local seismicity beneath the region from southern peru to northern chile the nazca plate descends with an almost constant dip angle 30 down to at least 300 km depth between the 30 dipping plate in southern peru and the horizontal profile beneath central peru there is a contortion over a 100 km wide continuous lateral section of the subducting plate we infer that at least in the upper 150 km depth range the descending nazca plate is contorted rather than torn

spatial distribution and b value of intermediate depth earthquakes beneath central peru we have investigated the spatial distribution of microseismicity at intermediate depth in the wadati benioff w b zone beneath central peru within a 100 to 150 km depth range in the subducting nazca plate 67 event hypocenters define a horizontally subducting zone horizontal zone 450 to 600 km from the trench and a zone of increasing dip resubduction zone 600 to 700 km from the trench although the shape of the w b zone is generally consistent with previous observations from teleseismic data the distribution of seismicity is not in a 550 km wide band extending from 400 to 750 km from the trench the density of teleseismicity mb 4 1971 1981 increases as a function of distance from the trench while the density of microseismicity 1 6 mb 4 2 decreases combining local and teleseismic data the b value changes from 84 in the horizontal zone to 57 in the resubduction zone this result suggests that the minimum earthquake size and or stress drop increases in the resubduction zone low b values may also be intrinsic to proximity to the seismic cut off at 150 km depth

the adriatic region an independent microplate within the africa eurasia collision zone 1 we use gps measurements and block modeling to investigate the present day deformation of the adriatic region whose kinematics within the nubia eurasia plate boundary zone is not well constrained and remains controversial block modeling allows us to compute rigid plate angular velocities while accounting for elastic strain accumulation along block bounding faults results suggest that the adriatic is a microplate adria and that the southern boundary with the nubia plate and the aegean domain may be located along the apulia escarpment and the kefallinia fault geodetic data alone cannot discriminate between a single block ap or a two blocks gdap description of adria but the gdap model predicts boundary slip rates that are in better agreement with observations from previous studies

current strain regime in the western alps from continuous global positioning system measurements 1996 2001 four to six years of continuous measurements at 10 permanent global positioning system sites in the western alps show horizontal residual velocities of 2 mm yr with respect to stable europe uncertainties range from 0 3 to 1 4 mm yr these velocities and the associated strain rate field indicate that the central part of the range is currently dominated by east west extension whereas the southern part shows north south to northwest southeast compression the geodetic and seismotectonic data are consistent with a model where strain is essentially controlled by the counterclockwise rotation of the adriatic microplate with respect to eurasia this rotation together with the arcuate shape of the contact between the adriatic microplate and the alps induces dextral shear kinematic boundary conditions across the western alps with an additional divergence component in their central part and in switzerland and a convergence component in their southern part

present state of tectonic stress of the friuli area eastern southern alps stress orientations are determined for the friuli area from focal mechanisms using the inversion technique of gephart and forsyth 1984 the data consist of 244 fault plane solutions selected for the period 1988 1995 where the data coverage was poor this period was extended to 1978 1996 local magnitude ranges from 2 0 to 4 3 and the depths extend from 4 to 16 km the friuli area is subdivided into five seismotectonic zones on the basis of tectonic characteristics seismic activity and focal mechanisms and for each zone a stress tensor is determined the results show that the active tectonic stress in the friuli area is heterogeneous and conditioned by the complex structural pattern which is characterized by two indented tectonic wedges the western and central parts of the area are mainly affected by a compressional state of stress while in the eastern part a strike slip state of stress prevails the orientation of the principal stresses varies from the western to the eastern part of the area and differences are also noticeable with depth in the central part of the friuli area the maximum compressional stress is n s trending at shallow depths 10 km changing to nw se at deeper levels the maximum compressional stress is nw se oriented in the western part while in the eastern part it is n s oriented

the subduction of young lithosphere studies using a variety of techniques of the subduction beneath western south america and the southwest honshu kyushu region of japan indicate that volcano free segments occur where the subducted and continental lithospheres remain in contact without intervening asthenosphere the subduction is initiated at normal dip angles but the plate deforms at some depth 100 km under central peru to travel horizontally immediately beneath continental lithosphere the most plausible reason for this geometry is that the subducted plate is buoyant a model is developed constrained by age of the plate bathymetry and heat flow estimates of the density of oceanic plates as a function of age show that younger ocean floor may be less dense than the asthenosphere into which it subducts if the high density tranformation of crustal basalt to eclogite is retarded by low temperatures the plate can remain buoyant to considerable depth for long periods of time heat flow data from western south america are consistent with this model

tidal coulomb failure stresses in the northern andean intermediate depth seismic clusters implications for a possible correlation between tides and seismicity abstract a recent statistical analysis of the relationship between tides and seismic activity in colombia has suggested the existence of correlation anomalies for the case of intermediate depth events in the bucaramanga nest and the cauca cluster moncayo et al 2019 in this work we explore in detail the hypothesis that tides may be triggering seismic activity in these regions and extend the analysis to two other seismic clusters in northern central south america specifically in the areas of el puyo ecuador and pucallpa peru for this purpose we use the available focal mechanism information for seismic events at these locations and calculate for each event the tidal coulomb failure stress tcfs as obtained from estimations of the tidal strain tensor tidal strains are computed considering the earth body tides and the effect of the ocean tidal loading since our purpose is to elucidate the role of tides in earthquake nucleation calculations of the tcfs are conducted not only for the time of earthquake but also for the time of the closest maximum strain within a window of a few hours before the events our results tend to support the hypothesis that tidal stresses are contributing to earthquake generation in all the studied areas this trend is especially stronger when tcfs are calculated at pre earthquake times the physical explanation for the positive contribution of tides to earthquake triggering in intermediate depth clusters may lie in the fact that a wide diversity of fault plane orientations is possible within a relatively small volume of subducted lithosphere so making the tides more likely to help loosening up the blocks at the fault plane to promote slip

magnitude frequency relations for northeastern japan magnitude frequency relations are investigated for the on land area covered by the tohoku university seismic network northeastern japan we combine the japan meteorological agency jma catalog with the tohoku university catalog for the crustal events the suite for the upper plane events of the double planed wadati benioff zone from 60 km through 100 km deep is based on the tohoku university catalog only completeness analyses of the catalog reveal that the crustal events and the upper plane events suite is complete down to magnitude 2 0 and 2 1 respectively including events only with magnitude above the completeness threshold the magnitude frequency relations are found to be nonlinear both for the crustal events slightly and the upper plane events strongly consistency between total seismic wave duration magnitudes and velocity amplitude magnitudes suggests that the magnitude scale in the catalog is nonbiased the completeness analyses and the non biased magnitude scale suggest that the nonlinear magnitude frequency relations are not artificial but substantial features of the earthquake occurrence

frequency distribution and quantification of deep earthquakes the frequency distribution of deep earthquakes d 350 km is analyzed on a regional scale using magnitude data from 4660 events reported in the international seismological center bulletin 1964 1982 and 391 centroid moment tensor solutions 1977 1987 we use the moment magnitude mw to define b values comparable with studies of shallow seismicity scaling laws relating mw mb and mo are derived mw 1 6mb 3 2 mb log mo 4 3 2 4 which compare very favorably with published laws uncertainties and biases of the mb and mo data sets are considered the slope of the frequency distribution is evaluated over a restricted magnitude range the results are very robust and independent from the magnitude range used from the mb magnitude data we obtain regional b values in the range 0 4 b 1 22 with a worldwide average value b 0 87 these results are confirmed by the analysis of the seismic moment data the steepest frequency distribution is observed in the tonga islands region b 1 22 although 60 of the worldwide deep seismicity occurs here only few events since 1977 had seismic moment exceeding 1019 n m the high fractal dimension d 2 4 implies a volume partially filled with fault planes in agreement with the observations on the seismic morphology of the region at the other extreme south america is characterized by the largest recorded deep events and an almost complete absence of small ones b 0 4

subcrustal earthquakes in the northern apennines italy evidence for a still active subduction previously unreported subcrustal earthquakes have been located up to 90 km depth beneath the northern apennines italy these earthquakes occur beneath a zone of abundant upper crustal seismicity mostly confined to the upper 20 km of the crust although there are relatively few well located subcrustal earthquakes there appears to be a general southwestward deepening of the hypocenters from the adriatic to the tyrrhenian sea consistent with other geophysical data which suggest that the adriatic lithosphere is presently subducting beneath the northern apennines

the hydrology of interconnected bog complexes in discontinuous permafrost terrains in the zone of discontinuous permafrost the cycling and storage of water within and between wetlands is poorly understood the presence of intermittent permafrost bodies tends to impede and re direct the flow of water in this region the landscape is characterized by forested peat plateaus that are underlain by permafrost and are interspersed by permafrost free wetlands these include channel fens which convey water to the basin outlet through wide hydraulically rough channels and flat bogs which are typically thought to retain moisture inputs as storage field studies conducted at a peatland dominated landscape near fort simpson northwest territories canada indicate the presence of ephemeral drainage channels that form a cascade of connected bogs that ultimately discharges into a channel fen consequently understanding bogs as dynamic transmitters of surface and subsurface flows rather than simple storage regions calls for further examination whether bogs act as either storage features or flow through features has a direct impact on the runoff contributing area in a basin here two adjacent series of bog cascades were gauged over two consecutive years to determine spatial and temporal changes in effective runoff contributing areas it was found that runoff varies significantly between two adjacent bog cascades with one cascade producing 125 mm of runoff over the 2 year period while the other yielded only 25 mm the bog cascades are primarily active during the snowmelt season when moisture conditions are high however flows can also be generated in response to large rain events it is proposed that bog cascades operate under an element threshold concept whereby in order for water to be transmitted through a bog the depression storage capacity of that bog must first be satisfied our work indicates that whether bogs act as storage features or flow through features has a direct impact on the runoff contributing area in a basin neglecting to represent connected bogs as dynamic transmission features in the landscape is shown to underestimate water available for streamflow by between 5 and 15 and these systems are therefore a key component of the water balance in discontinuous permafrost regions copyright 2015 john wiley sons ltd