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

the oaxaca mexico earthquake of 1931 lithospheric normal faulting in the subducted cocos plate a study of the great earthquake in oaxaca mexico on 15 january 1931 shows that it was a normal fault earthquake striking east west the lack of evidence of surface faulting near the source region1 and the focal depth of 40 km inferred from body wave modelling suggest that the earthquake occurred within the subducted slab the large size of the earthquake ms 8 0 strongly suggests that the rupture broke through the entire lithosphere of the subducted cocos plate other large normal fault earthquakes in the japanese2 aleutian3 peruvian4 and sumba5 arcs show lithospheric faulting seawards of the trench or very close to it the 1931 event however occurred farther down dip in the slab 150 km landward of the trench below the bottom of what appears to be the seismogenic plate interface we speculate here that large although infrequent normal fault earthquakes such as the 1931 oaxaca earthquake may have a role in decoupling at depth the subducted slab from the upper part of the slab and perhaps from the overriding mexican continental plate the epicentral location of the 1858 michoacan earthquake6 ms 7 5 suggests that it may represent another example of lithospheric normal faulting in the middle american arc such earthquakes for which the periods of recurrence are unknown constitute an extremely high seismic risk to population centres of mexico

source characteristics of large deep earthquakes constraint on the faulting mechanism at great depths 1 source parameters for eight large deep earthquakes are inferred from broadband data of the global seismograph network we completed an unprecedented data set composed of 14 largest deep earthquakes mw ranging from 7 0 to 8 3 from six different subduction zones studied with identical source parameter inversion methods the study confirms earlier findings that deep earthquake source properties vary with the temperature of the subducting plate events in cold slabs show high aftershock activity high rupture velocity and high seismic efficiency in contrast earthquakes in warm slabs generally have low aftershock productivity low rupture velocity and low seismic efficiency however the 23 june 1991 argentina event has source properties that are rather characteristic for earthquakes in cold slabs and that differ from those of other large south american events we suggest that two types of deep earthquakes occur in south america and we interpret these results in the context of the shear instability model for the mechanism of deep earthquakes in this model shear failure occurs through a thermal runaway mechanism within a shear zone at great depth and low seismic efficiency might indicate significant energy dissipation due to heating and possible melt production the 1991 argentina event located in a pocket of deep seismicity within the slab core may represent a shear instability with little melting as would be the case for large deep earthquakes in cold subduction zones whereas the other known south american large deep events such as 1963 peru 1970 colombia and 1994 bolivia are located in relatively aseismic regions and may involve significant melting within warmer regions of the slab

remote triggering of deep earthquakes in the 2002 tonga sequences it is well established that an earthquake in the earth s crust can trigger subsequent earthquakes but such triggering has not been documented for deeper earthquakes models for shallow fault interactions suggest that static permanent stress changes can trigger nearby earthquakes within a few fault lengths from the causative earthquake1 2 3 whereas dynamic transient stresses carried by seismic waves may trigger earthquakes both nearby and at remote distances4 5 6 7 8 here we present a detailed analysis of the 19 august 2002 tonga deep earthquake sequences and show evidence for both static and dynamic triggering seven minutes after a magnitude 7 6 earthquake occurred at a depth of 598 km a magnitude 7 7 earthquake 664 km depth occurred 300 km away in a previously aseismic region we found that nearby aftershocks of the first mainshock are preferentially located in regions where static stresses are predicted to have been enhanced by the mainshock but the second mainshock and other triggered events are located at larger distances where static stress increases should be negligible thus suggesting dynamic triggering the origin times of the triggered events do not correspond to arrival times of the main seismic waves from the mainshocks and the dynamically triggered earthquakes frequently occur in aseismic regions below or adjacent to the seismic zone we propose that these events are triggered by transient effects in regions near criticality but where earthquakes have difficulty nucleating without external influences

a hybrid method for calculating the radiated wave energy of deep earthquakes abstract the energy radiated as waves is a parameter vital to the understanding of earthquake rupture physics calculations of this energy however are difficult and wrought with uncertainty we developed a new hybrid method for the calculation of radiated wave energy and other key seismic parameters the method calculates these parameters in an internally consistent and objective manner allowing for robust comparison between parameters and across earthquakes in addition the method does not require deconvolution or filtering of data thus results contain all recorded high frequencies we use the method to calculate source time functions seismic moment duration and radiated wave energy for 19 recent deep depth 292 km earthquakes ranging in size from m w 6 5 to 8 2 we compute effective seismic efficiency for the three largest events the principle result is that the effective seismic efficiencies are less than 0 3 if earthquake rupture adhered to the orowan model then the average frictional stress during rupture is equal to the final shear stress on the fault plane and the seismic efficiency is 1 but since the measured seismic efficiency is less than 1 the rupture process of these large deep earthquakes partitions more energy into friction and the average frictional stress during rupture is higher than the final fault plane stress

well catchments and time of travel zones in aquifers with recharge the classical analytical method used to map catchments and time of travel zones of pumping wells was originally derived for another purpose and takes no account of recharge bear and jacobs 1965 generalized catchment shapes are presented here for aquifers with recharge they can be scaled to field situations through two or three nondimensional parameters a semianalytical path line tracing model was used to generate the shapes it contains new expressions for pore water velocities in two infinite strip recharged aquifers one with two fixed head boundaries the other with one impermeable boundary the resulting catchments differ significantly in both shape and size from catchments estimated by the no recharge method generalized results are also presented for time of travel zones which are noticeably smaller than those calculated by the no recharge method comparison with an equivalent recently released model from the u s environmental protection agency shows the latter to give poor estimates of catchments and time of travel zones

magnitudes of large shallow earthquakes from 1904 to 1980 abstract in order to obtain a uniform magnitude catalogue surface wave magnitudes ms and broad band body wave magnitudes mb have been determined for large shallow earthquakes from 1904 to 1980 in making the catalogue homogeneous the author consistently adheres to the original definitions of ms and mb given by gutenberg 1945 and gutenberg and richter 1956 the determinations of ms and mb are all based on the amplitude and period data listed in gutenberg and richter s unpublished notes bulletins from stations worldwide and other basic information mb is measured on broad band instruments in periods of 8 s consistency of the magnitude determinations from these different sources is carefully checked in detail more than 900 shallow shocks of magnitude 7 and over are catalogued the meaning of the magnitude scales in various catalogues is examined in terms of ms and mb most of the magnitudes listed by gutenberg and richter 1954 in their seismicity of the earth are basically ms for large shocks shallower than 40 km but are basically mb for large shocks at depths of 40 60 km the surface wave magnitudes given by earthquake data reports are higher than ms by 0 2 unit whether the combined horizontal amplitude or the vertical amplitude is used mb and the currently used 1 s body wave magnitude are measured at different periods and should not be directly compared

analytical solution for capture and catchment zones of a well located on a groundwater divide 1 an analytical solution is presented for capture and catchment zones of a well located on a groundwater divide in a recharged aquifer the analytical solution is derived for a homogeneous isotropic and uniformly thick leaky aquifer it is shown that streamlines and well catchment area have elongated shapes tending to infinity along the groundwater divide and do not depend on any aquifer property but only on the ratio of the well pumping rate and aquifer recharge flux isochrones delineating capture zones also depend on the mean residence time of the groundwater which is independent of the well pumping rate the capture and catchment zones differ significantly in both size and shape from the classical theory that ignores recharge in particular the catchment zone is wider and has a finite extent

capture zone between two streams summary we have investigated stream aquifer interaction with a single pumping well in an aquifer bounded by two parallel nearby streams this study presents steady state semi analytical solutions to calculate the fraction of water withdrawal from two streams potential theory is used to describe the capture zone between two streams when low permeability streambeds are not present steady state flow equations in the aquifer and two streambeds are solved following rigorous mass balance requirements if low permeability streambeds are present when the low permeability streambeds are not present and the regional flow exists between two streams this study finds that the maximal capture size without extracting water from the down gradient stream decreases with the normalized well location in an approximately linear fashion furthermore the normalized flux from the up gradient stream decreases with the normalized well location faster than the linear fashion when the low permeability streambeds exist and the regional flow is neglected the normalized flux across either streambed varies with the normalized well location in a linear function furthermore the magnitude of the slope of that function is nearly unity when the hydraulic conductance ratio of the two streambeds is one and is less than unity when the hydraulic conductance ratio of the two streambeds is either greater or smaller than one when the normalized well location with equal fluxes from two streams versus the hydraulic conductance ratio of the two streambeds are plotted semi logarithmically we observed a segmented curve including a steep segment at the beginning followed by a flat segment and a final steep segment

global evaluation of large earthquake energy from 1997 through mid 2010 1 we develop an updated radiated seismic energy e catalog of global earthquakes with seismic moment m0 1019 nm mw 6 7 from 1997 through mid 2010 recording 342 events using 17849 seismograms station specific corrections and event duration dependent total p wave group calculations allow for improved e determinations for large and long duration earthquakes we find the global mean energy to moment ratio log10 e m0 4 59 0 36 robust deviations are found for thrust t 4 74 strike slip ss 4 44 and normal n 4 51 faulting events for two regions with recent energy deficient tsunami earthquakes tse we examine all large thrust earthquakes with m0 5 1017 nm mw 5 7 to identify a regional characterization in their relative radiated energy to moment ratio while thrust events along java indonesia the site of two tse events in 1994 and 2006 are comparable t jv 4 91 to the global thrust average events along the middle america trench mat the site of the 1992 nicaragua tse are consistently deficient t mat 5 15 along the mat a trend of increased deficiency in radiated energy to the southeast occurs in the direction of more rapid plate convergence global thrust mechanisms become increasingly deficient in radiated seismic energy at shallow depths with tse events representing the shallowest and most energetically deficient end member of the events in the study results suggest thrust events are highly variable but tend to increase in apparent stress from about 15 kpa near the surface to 2 mpa near 70 km depth

hydrodynamics of the capture zone of a partially penetrating well in a confined aquifer in the pump and treat approach to the problem of managing a contaminated aquifer a key problem is to design an effective capture system that collects only the polluted groundwater without allowing any of it to escape at present it is customary to design a capture system using fully penetrating withdrawal wells very often however only part of the vertical thickness of the aquifer is contaminated so the question may arise whether a more efficient capture system can be achieved using partially penetrating wells very little work has been done on the application of partially penetrating wells to this problem a new semianalytic method that can be used in determining the geometry of the capture zone for steady state flow to a partially penetrating well that is screened from the top or from the bottom of a confined aquifer has been developed by combining the velocity potentials for flow to the well with that for the regional flow field a three dimensional velocity potential that can be used in determining the complete geometry of the capture surface has been developed the results have shown that with a constant pumping rate the maximum horizontal extent of the capture surface at the top or bottom of the aquifer increases as the degree of penetration decreases as one would expect the maximum vertical extent increases as the depth of penetration increases thus if one knows the actual location of the contaminant plume an appropriate combination of the degree of penetration and pumping rate can be selected to create an effective capture zone

comprehensive analysis of earthquake source spectra in southern california we compute and analyze p wave spectra from earthquakes in southern california between 1989 and 2001 using a method that isolates source receiver and path dependent terms we correct observed source spectra for attenuation using both fixed and spatially varying empirical green s function methods estimated brune type stress drops for over 60 000 m l 1 5 to 3 1 earthquakes range from 0 2 to 20 mpa with no dependence on moment or local b value median computed stress drop increases with depth in the upper crust from about 0 6 mpa at the surface to about 2 2 mpa at 8 km where it levels off and remains nearly constant in the midcrust down to about 20 km however the results at shallow depths could also be explained as reduced rupture velocities near the surface rather than a change in stress drop spatially coherent variations in median stress drop are observed with generally low values for the imperial valley and northridge aftershocks and higher values for the eastern transverse ranges and the north end of the san jacinto fault we find no correlation between observed stress drop and distance from the san andreas and other major faults significant along strike variations in stress drop exist for aftershocks of the 1992 landers earthquake which may correlate with differences in main shock slip

the isc gem global instrumental earthquake catalogue 1900 2009 introduction abstract in this introductory article we give a general description of the isc gem global instrumental earthquake catalogue 1900 2009 we also provide the background for four further articles that describe the effort in collecting and digitizing parametric earthquake bulletin data as well as the methodologies developed to compute homogeneous earthquake parameters the result of the two and a half year project is a catalogue of approximately 20 000 large earthquakes covering 110 years with hypocentres and uncertainties computed using the same technique and velocity model we show that the overall homogeneity of the main earthquake parameters in the catalogue was achieved despite changes in instrumentation and routine measurement practices concurrent with developments in instrumental seismology from almost a ground level to its current state for each earthquake mw magnitude values and uncertainties were computed either based on available estimates of seismic moment or using new empirical relationships between mw ms and mb further important results of this project include the electronic availability of a considerable volume of seismic wave arrival time and amplitude measurements from early instrumental printed station bulletins these newly recovered amplitude measurements provided a basis for computation of many previously unavailable ms magnitudes with uncertainties in this article we describe why such a catalogue is required for a comprehensive assessment of global and regional seismic hazard we also describe other potential uses of the catalogue in many other fields of earth sciences we discuss the catalogue availability and lay out the plans of further development

tsunami earthquakes slow thrust faulting events in the accretionary wedge the november 20 1960 peru october 20 1963 kurile and june 10 1975 kurile earthquakes are classified as tsunami earthquakes based on anomalously large tsunami excitation relative to earthquake magnitude long period surface wave analysis indicates double couple faulting mechanisms for all three events rather than single force mechanisms indicative of submarine landslides the earthquakes have shallow depths 15 km and are located near the trench axis and seaward of most other thrust zone events beneath the accretionary prism body waveform inversion indicates very shallowly dipping thrust faulting mechanisms for the three events with dip angles of 6 8 surface wave spectral amplitudes and deconvolution of sh waveforms suggests anomalously long source durations and large seismic moments relative to ms specifically the 1963 kurile event ms 7 2 shows a duration of 85 s and a moment of 6 0 1027 dyn cm mw 7 8 the 1975 kurile event ms 7 0 shows a duration of 60 s and a moment of 2 0 1027 dyn cm mw 7 5 and the 1960 peru event ms 6 75 shows a time function consisting of four subevents with a total duration of 110 130 s and a seismic moment of 3 4 1027 dyn cm mw 7 6 estimated rupture velocities are about 1 km s or less but there is no evidence of unusually low stress drops the august 1 1968 philippines event previously classified as a tsunami earthquake shows none of the anomalous source properties and teleseismic tsunami height measurements are sparse we do not consider this event a tsunami earthquake most of the anomalous tsunami excitation results from underestimation of earthquake size by ms due to the long source duration the tsunami heights are not significantly anomalous relative to seismic moment the slow nature of these events may result from rupture through the sedimentary rock along the basal decollement of the accretionary prism standard scaling laws when adjusted for the slow seismic velocity in the source region show an mw ms relationship similar to that observed for the tsunami earthquakes and predict ms saturation at about 7 3 rather than 8 0 for typical events

sandbox models of relay ramp structure and evolution relay ramps are a common feature formed during the growth of normal fault systems we performed analogue experiments to investigate the structure and evolution of relay ramps an extending rubber sheet induces extension at the base of a sand pack brittle crust analogue silicone bars between the rubber and the sand control the location of fault nucleation we tested the role of fault spacing fault length overlap length and fault strike in the evolution of relay ramps the modelled relay ramps evolved in three stages characterized by the growth of the normal faults their interaction and linkage interaction and linkage occurred only when the combined length of the two interacting faults was larger than eight times their spacing the length to width ratio of the relay ramps during the interaction stage showed preferred geometries clustering around three the propagation of the fault tips was observed both before and after the linkage stage overlap length and spacing relations of the modelled relay ramps are similar to those in nature at different scales and can be explained using existing mechanical models nevertheless the further propagation of the fault tips after linkage has not been described previously

supershear rupture in the 24 may 2013 mw 6 7 okhotsk deep earthquake additional evidence from regional seismic stations zhan et al 2014a reported supershear rupture during the m w 6 7 aftershock of the 2013 m w 8 3 sea of okhotsk deep earthquake relying heavily on the regional station pet which played a critical role in constraining the vertical rupture dimension and rupture speed here we include five more regional stations and find that the durations of the source time functions derived from these stations are consistent with zhan et al s supershear rupture model furthermore to reduce the nonuniqueness of deconvolution and combine the bandwidths of different stations we conduct a joint inversion of the six regional stations for a single broadband moment rate function mrf the best fitting mrf which explains all the regional waveforms well has a smooth shape without any temporal gaps the m w 6 7 okhotsk deep earthquake is more likely a continuous supershear rupture than a dynamically triggered doublet

seismic constraints on mechanisms of deep earthquake rupture 1 observations of the depth distribution of seismicity suggest that several mechanisms cause deep earthquakes cold subducting slabs exhibit a broad peak in seismicity between 300 and 530 km depth that is best explained by transformational faulting of metastable olivine cumulative seismic moment release increases sharply at 530 km depth in both cold and warm slabs implying that events deeper than this are controlled by an equilibrium rather than a metastable phase change which would be temperature dependent this together with the observation that deep seismicity predominates near the garnet rich upper boundary of the subducting plate former oceanic crust suggests that the transformation of garnet to perovskite which may release considerable water is integral in the cause of earthquakes deeper than 530 km where most deep earthquakes occur

analytical solution for the catchment zone of a well located near a groundwater divide in a recharged semi confined aquifer summary an analytical solution is presented for delineating the catchment zone of a well located near a groundwater divide in a recharged aquifer the analytical solution is derived for an infinitely wide homogeneous isotropic and uniformly thick semi confined aquifer it is shown that the shape and extent of the well catchment zone only depend on the distance to the groundwater divide and on the ratio of the well pumping and groundwater recharge rates the catchment zone of a pumping well extends beyond the groundwater divide such that the total area affected at the other side of the groundwater divide equals one half of the well catchment area and consists of a part from which groundwater is captured by the well and another part from which groundwater is flowing to the other side but bypassing the well the amount of groundwater transfer involved equals half of the pumping rate in case of an injection well the catchment zone comprises the whole aquifer when the well is sufficiently close to the groundwater divide and otherwise consist of an infinite but laterally bounded zone in the direction away from the groundwater divide in both cases the aquifer at the other side of the groundwater divide gains half of the well injection rate either directly by flow from the injection well or indirectly by capturing groundwater recharge from the other side of the groundwater divide

an analytical solution for the capture zone of two arbitrarily located wells abstract a capture zone of pumping well s in an aquifer with regional groundwater flow has been widely used to help design a pump and treat system for groundwater containment and remediation based on the theorem of potential and the principle of superposition an analytical solution is derived in this study to calculate the capture zone for two arbitrarily located wells that pump water from a confined aquifer at an equal flow rate the general two well capture zone is composed of two sub capture zones one for each well the shapes of the two sub capture zones and their relative locations change with variations of the orientation and the separation of the two wells the solution can be useful in verifying available numerical codes as well as in solving practical field problems

rupture complexity of the 1994 bolivia and 2013 sea of okhotsk deep earthquakes the physical mechanism of deep earthquakes depth 300 km remains enigmatic partly because their rupture dimensions are difficult to estimate due to their low aftershock productivity and absence of geodetic or surface rupture observations the two largest deep earthquakes the recent great 2013 sea of okhotsk earthquake m 8 3 depth 607 km and the great 1994 bolivia earthquake m 8 3 depth 637 km together provide a unique opportunity to compare their rupture patterns in detail here we extend a travel time sub event location method to perform full teleseismic p waveform inversion this new method allows us to explain the observed broadband records with a set of sub events whose model parameters are robustly constrained without smoothing we find that while the okhotsk event is mostly unilateral rupturing 90 km along strike with a velocity over 4 km s the bolivia earthquake ruptured about half this distance at a slow velocity about 1 5 km s and displayed a major change in rupture direction we explain the observed differences between the two earthquakes as resulting from two fundamentally different faulting mechanisms in slabs with different thermal states phase transformational faulting is inferred to occur inside the metastable olivine wedge within cold slab cores whereas shear melting occurs inside warm slabs once triggered