The Experts below are selected from a list of 306 Experts worldwide ranked by ideXlab platform
Hiroo Kanamori - One of the best experts on this subject based on the ideXlab platform.
-
estimation of Radiated Energy using the kik net downhole records old method for modern data
Geophysical Journal International, 2020Co-Authors: Hiroo Kanamori, Zachary E Ross, Luis RiveraAbstract:We use KiK-net (NIED) down hole records to estimate the Radiated Energy,ER, of 29 Japanese inland earthquakes with a magnitude range from Mw=5.6 to 7.0. The method is based on the work of Gutenberg and Richter in which the time integral of S-wave ground-motion velocity-squared is measured as a basic metric of the Radiated Energy. Only stations within a distance of 100 km are used to minimize complex path and attenuation effects. Unlike the teleseismic method that uses mainly P waves, the use of S waves which carry more than 95 per cent of the Radiated Energy allows us to obtain robust results. We calibrate the method using synthetic seismograms to modernize and improve the Gutenberg–Richter method. We compute synthetic seismograms for a source model of each event with a given source function (i.e. known ER), the actual mechanism and the source-station geometry. Then, we compare the given ER with the computed Energy metric to correct for the unknown effect of wave propagation and the mechanism. The use of down hole records minimizes the uncertainty resulting from the site response. Our results suggest that the currently available estimates of ER from teleseismic data are probably within a factor of 3, on average, of the absolute value. The scaled Energy eR(=ER/M0) is nearly constant at about 3×10**(−5) over a magnitude range from Mw=5.6 to 7.0 with a slight increasing trend with Mw. We found no significant difference in eR between dip-slip and strike-slip events.
-
rupture characteristics of major and great mw 7 0 megathrust earthquakes from 1990 to 2015 1 source parameter scaling relationships
Journal of Geophysical Research, 2016Co-Authors: Thorne Lay, Hiroo Kanamori, Luis RiveraAbstract:Source parameter scaling for major and great thrust-faulting events on circum-Pacific megathrusts is examined using uniformly processed finite-fault inversions and Radiated Energy estimates for 114 M_w ≥ 7.0 earthquakes. To address the limited resolution of source spatial extent and rupture expansion velocity (V_r) from teleseismic observations, the events are subdivided into either group 1 (18 events) having independent constraints on V_r from prior studies or group 2 (96 events) lacking independent V_r constraints. For group 2, finite-fault inversions with V_r = 2.0, 2.5, and 3.0 km/s are performed. The product V_r^3Δσ_E, with stress drop Δσ_E calculated for the slip distribution in the inverted finite-fault models, is very stable for each event across the suite of models considered. It has little trend with M_w, although there is a baseline shift to low values for large tsunami earthquakes. Source centroid time (T_c) and duration (T_d), measured from the finite-fault moment rate functions vary systematically with the cube root of seismic moment (M_0), independent of assumed V_r. There is no strong dependence on magnitude or Vr for moment-scaled Radiated Energy (E_R/M_0) or apparent stress (σ_a). Δσ_E averages ~4 MPa, with direct trade-off between V_r and estimated stress drop but little dependence on M_w. Similar behavior is found for radiation efficiency (η_R). We use V_r^3Δσ_E and T_c/M_0^(1/3) to explore variation of stress drop, V_r and radiation efficiency, along with finite-source geometrical factors. Radiation efficiency tends to decrease with average slip for these very large events, and fracture Energy increases steadily with slip.
-
Radiated Energy and the physics of earthquake faulting
Eos Transactions American Geophysical Union, 2005Co-Authors: A Mcgarr, Rachel E. Abercrombie, Hiroo KanamoriAbstract:On the third day of a recent AGU Chapman Conference, held in Portland, Maine, near the Two Lights fault zones and the Fort Foster brittle zone, conference participants spent the gray June day scrambling over rocky ledges above the crashing surf along the coast of the Atlantic Ocean. With field trip leader Mark Swanson, who with his students has studied the area in detail over the past 20 years, participants examined evidence of ancient earthquakes from about 300 million years ago when these rocks were 8 to 10 kilometers deep. This evidence included pseudotachylytes—glass generated by heating during fault slip at midcrustal depths.
-
Representations of the Radiated Energy in Earthquakes
2004Co-Authors: Luis Rivera, Hiroo KanamoriAbstract:We investigate the representation of the Radiated Energy, E_R, in earthquakes. In seismology E_R is estimated from either far-field seismic waves or the stress and displacement on the fault plane. Although E_R comes from the entire volume of the Earth, it can be expressed as an integral over the fault plane. However, the integrand cannot be given a simple physical meaning such as the Radiated Energy density on the fault plane. The stress on the fault plane changes rapidly during a seismic rupture. Although the Energy Radiated by this process is not included in the estimate of E_R in a simplified practice in seismology, it is correctly included in the expression of E_R in standard seismological practice. Using the representation theorem, we can express E_R as a surface integral over the fault plane, with the integrand containing the slip function on the fault plane. However, the integrand at a point depends not only on the slip function at the point but also on the slip functions everywhere on the fault plane. Thus, the simple method in which E_R is estimated by summation of the local Energy flux on the fault plane does not yield a correct estimate.
-
observational constraints on the fracture Energy of subduction zone earthquakes
Journal of Geophysical Research, 2004Co-Authors: Anupama Venkataraman, Hiroo KanamoriAbstract:We relate seismologically observable parameters such as Radiated Energy, seismic moment, rupture area, and rupture speed to the dynamics of faulting. To achieve this objective, we computed the Radiated Energy for 23 subduction zone earthquakes recorded between 1992 and 2001; most of these earthquakes have a magnitude M_w > 7.5, but we also included some smaller (M_w ∼ 6.7) well-studied subduction zone earthquakes and six crustal earthquakes. We compiled static stress drop estimates for these 29 earthquakes from literature and used a slip-weakening model to determine the radiation efficiency of these earthquakes. We also determined the rupture speed of these earthquakes from literature. From fracture mechanics, fracture Energy, and hence radiation efficiency, can be related to the rupture speed. The radiation efficiencies estimated from the partitioning of Energy as given by the slip-weakening model are consistent with the rupture speed estimated for these earthquakes. Most earthquakes have radiation efficiencies between 0.25 and 1 and are hence efficient in generating seismic waves, but tsunami earthquakes and two deep earthquakes, the 1994 Bolivia and the 1999 Russia-China border earthquakes, have very small radiation efficiencies (<0.25) and hence dissipate a large amount of Energy during faulting. We suggest that differences in the radiation efficiencies of different types of earthquakes could be due to fundamental differences in their rupture mechanics. In deep events, the Energy is probably dissipated in thermal processes in the fault zone, while it is possible that the morphology of the trench causes large Energy dissipation during the rupture process of tsunami earthquakes.
John Boatwright - One of the best experts on this subject based on the ideXlab platform.
-
Earthquakes: Radiated Energy and the Physics of Faulting - A Brief Review of Techniques Used to Estimate Radiated Seismic Energy
Geophysical monograph, 2013Co-Authors: Anupama Venkataraman, Gregory C. Beroza, John BoatwrightAbstract:Seismic Energy is a fundamental parameter of the earthquake source. Different parts of the seismogram and different techniques can be used to estimate the Radiated Energy, often with very different results. In this paper, we briefly review key techniques and compare their advantages and disadvantages. We divide the methods based on the wave types used. In order to understand the factors that control the Radiated seismic Energy, and what any observed variations in radiation efficiency with earthquake size might mean, we also need to measure other macroscopic parameters of the earthquake source, such as the static stress drop and the rupture velocity. Measuring these parameters accurately, especially for small earthquakes, is a challenging problem that needs to be addressed in future studies.
-
an overview of the global variability in Radiated Energy and apparent stress
Geophysical monograph, 2013Co-Authors: George L Choy, A Mcgarr, Stephen H Kirby, John BoatwrightAbstract:A global study of Radiated seismic energies E R and apparent stresses T a reveals systematic patterns. Earthquakes with the highest apparent stress occur in regions of intense deformation and rupture strong lithosphere. In oceanic settings, these are strike-slip earthquakes (T a up to 27 MPa) occurring intraplate or at evolving ends of transform faults. At subduction zones and intracontinental settings, these are strike-slip earthquakes with T a up to 7 MPa. Normal-fault earthquakes exhibit a more complex pattern. Higher T a 's (up to 5 MPa) are found for intraslab events at depths from 35 to 70 km that occur near zones of intense deformation such as a sharp slab bend or the juncture of colliding slabs. Lower T a 's (< 1 MPa) are found for normal-fault earthquakes at the outer rise and outer trench wall or deep in flat warm slabs. The lowest average τ a (0.3 MPa) is found for thrust-fault earthquakes at subduction zones. The variation of average apparent stress with tectonics suggests a relationship with lithospheric strength and fault maturity. Mature faults, such as plate boundaries that have experienced large cumulative slip, appear to have low strength and tend to yield earthquakes with low apparent stresses. Immature faults, in contrast, are stronger and yield high apparent stresses because either they are the result of fresh-rock fracture or at least their cumulative fault slip is quite small. These results have implications of use to the seismic engineering community because E R and its magnitude counterpart M e are reliable indicators of the potential for damaging ground motion.
-
Laboratory-Based Maximum Slip Rates in Earthquake Rupture Zones and Radiated Energy
Bulletin of the Seismological Society of America, 2010Co-Authors: Arthur F. Mcgarr, Joe B. Fletcher, Margaret S. Boettcher, Nicholas M. Beeler, John BoatwrightAbstract:Laboratory stick-slip friction experiments indicate that peak slip rates increase with the stresses loading the fault to cause rupture. If this applies also to earthquake fault zones, then the analysis of rupture processes is simplified inasmuch as the slip rates depend only on the local yield stress and are independent of factors specific to a particular event, including the distribution of slip in space and time. We test this hypothesis by first using it to develop an expression for Radiated Energy that depends primarily on the seismic moment and the maximum slip rate. From laboratory results, the maximum slip rate for any crustal earthquake, as well as various stress parameters including the yield stress, can be determined based on its seismic moment and the maximum slip within its rupture zone. After finding that our new equation for Radiated Energy works well for laboratory stick-slip friction experiments, we used it to estimate Radiated energies for five earthquakes with magnitudes near 2 that were induced in a deep gold mine, an M 2.1 repeating earthquake near the San Andreas Fault Observatory at Depth (SAFOD) site and seven major earthquakes in California and found good agreement with energies estimated independently from spectra of local and regional ground-motion data. Estimates of yield stress for the earthquakes in our study range from 12 MPa to 122 MPa with a median of 64 MPa. The lowest value was estimated for the 2004 M 6 Parkfield, California, earthquake whereas the nearby M 2.1 repeating earthquake, as recorded in the SAFOD pilot hole, showed a more typical yield stress of 64 MPa.
-
Radiated Energy and the rupture process of the denali fault earthquake sequence of 2002 from broadband teleseismic body waves
Bulletin of the Seismological Society of America, 2004Co-Authors: George L Choy, John BoatwrightAbstract:Displacement, velocity, and velocity-squared records of P and SH body waves recorded at teleseismic distances are analyzed to determine the rupture characteristics of the Denali fault, Alaska, earthquake of 3 November 2002 ( M W 7.9, M e 8.1). Three episodes of rupture can be identified from broadband (∼0.1–5.0 Hz) waveforms. The Denali fault earthquake started as a M W 7.3 thrust event. Subsequent right-lateral strike-slip rupture events with centroid depths of 9 km occurred about 22 and 49 sec later. The teleseismic P waves are dominated by Energy at intermediate frequencies (0.1–1 Hz) Radiated by the thrust event, while the SH waves are dominated by Energy at lower frequencies (0.05–0.2 Hz) Radiated by the strike-slip events. The strike-slip events exhibit strong directivity in the teleseismic SH waves. Correcting the recorded P -wave acceleration spectra for the effect of the free surface yields an estimate of 2.8 × 10 15 N m for the Energy Radiated by the thrust event. Correcting the recorded SH -wave acceleration spectra similarly yields an estimate of 3.3 × 10 16 N m for the Energy Radiated by the two strike-slip events. The average rupture velocity for the strike-slip rupture process is 1.1 β –1.2 β . The strike-slip events were located 90 and 188 km east of the epicenter. The rupture length over which significant or resolvable Energy is Radiated is, thus, far shorter than the 340-km fault length over which surface displacements were observed. However, the seismic moment released by these three events, 4 × 10 20 N m, was approximately half the seismic moment determined from very low-frequency analyses of the earthquake. The difference in seismic moment can be reasonably attributed to slip on fault segments that did not radiate significant or coherent seismic Energy. These results suggest that very large and great strike-slip earthquakes can generate stress pulses that rapidly produce substantial slip with negligible stress drop and little discernible Radiated Energy on fault segments distant from the initial point of nucleation. The existence of this Energy-deficient rupture mode has important implications for the evaluation of the seismic hazard of very large strike-slip earthquakes.
-
regional estimates of Radiated seismic Energy
Bulletin of the Seismological Society of America, 2002Co-Authors: John Boatwright, George L Choy, Linda C SeekinsAbstract:We revise the spectral technique for estimating Radiated Energy from recordings of large earthquakes at regional distances (Δ 27.5 km from the source, we model the geometrical spreading of the regional wavefield as r – γ where γ = 0.5 for f ≤ 0.2 Hz and γ = 0.7 for f ≥ 0.25 Hz. We fit the spectral falloff with distance using a frequency-dependent attenuation Q = 400( f /1.5)0.6, where Q = 400 for f ≤ 1.5 Hz. There is little directivity apparent in the corrected velocity spectra: the velocity spectra observed to the northwest along strike are amplified by a factor of 2.5 from 0.3 to 1.0 Hz and those to the southeast are amplified by a factor of 1.6 from 0.3 to 0.7 Hz. We group the stations in NEHRP site classes, using average 1-D velocity structures to estimate site amplification as a function of frequency and assuming 0.40 ≤ κ ≤ 0.55 sec for the near-surface attenuation. We increase the amplification of the soft-soil sites from 0.1 to 1.0 Hz by a factor that reaches 1.7 at 0.3 Hz because they are more strongly amplified than the NEHRP-D velocity structure predicts. We combine the 65 single-station estimates of Radiated Energy using an equal-azimuth weighting scheme that compensates for station distribution and incorporates the observed directivity, yielding a regional estimate of E s = 3.4 ± 0.7 × 1022 dyne cm. This regional estimate of Radiated Energy corresponds closely to the teleseismic estimate of E s = 3.2 × 1022 dyne cm.
Luis Rivera - One of the best experts on this subject based on the ideXlab platform.
-
estimation of Radiated Energy using the kik net downhole records old method for modern data
Geophysical Journal International, 2020Co-Authors: Hiroo Kanamori, Zachary E Ross, Luis RiveraAbstract:We use KiK-net (NIED) down hole records to estimate the Radiated Energy,ER, of 29 Japanese inland earthquakes with a magnitude range from Mw=5.6 to 7.0. The method is based on the work of Gutenberg and Richter in which the time integral of S-wave ground-motion velocity-squared is measured as a basic metric of the Radiated Energy. Only stations within a distance of 100 km are used to minimize complex path and attenuation effects. Unlike the teleseismic method that uses mainly P waves, the use of S waves which carry more than 95 per cent of the Radiated Energy allows us to obtain robust results. We calibrate the method using synthetic seismograms to modernize and improve the Gutenberg–Richter method. We compute synthetic seismograms for a source model of each event with a given source function (i.e. known ER), the actual mechanism and the source-station geometry. Then, we compare the given ER with the computed Energy metric to correct for the unknown effect of wave propagation and the mechanism. The use of down hole records minimizes the uncertainty resulting from the site response. Our results suggest that the currently available estimates of ER from teleseismic data are probably within a factor of 3, on average, of the absolute value. The scaled Energy eR(=ER/M0) is nearly constant at about 3×10**(−5) over a magnitude range from Mw=5.6 to 7.0 with a slight increasing trend with Mw. We found no significant difference in eR between dip-slip and strike-slip events.
-
rupture characteristics of major and great mw 7 0 megathrust earthquakes from 1990 to 2015 1 source parameter scaling relationships
Journal of Geophysical Research, 2016Co-Authors: Thorne Lay, Hiroo Kanamori, Luis RiveraAbstract:Source parameter scaling for major and great thrust-faulting events on circum-Pacific megathrusts is examined using uniformly processed finite-fault inversions and Radiated Energy estimates for 114 M_w ≥ 7.0 earthquakes. To address the limited resolution of source spatial extent and rupture expansion velocity (V_r) from teleseismic observations, the events are subdivided into either group 1 (18 events) having independent constraints on V_r from prior studies or group 2 (96 events) lacking independent V_r constraints. For group 2, finite-fault inversions with V_r = 2.0, 2.5, and 3.0 km/s are performed. The product V_r^3Δσ_E, with stress drop Δσ_E calculated for the slip distribution in the inverted finite-fault models, is very stable for each event across the suite of models considered. It has little trend with M_w, although there is a baseline shift to low values for large tsunami earthquakes. Source centroid time (T_c) and duration (T_d), measured from the finite-fault moment rate functions vary systematically with the cube root of seismic moment (M_0), independent of assumed V_r. There is no strong dependence on magnitude or Vr for moment-scaled Radiated Energy (E_R/M_0) or apparent stress (σ_a). Δσ_E averages ~4 MPa, with direct trade-off between V_r and estimated stress drop but little dependence on M_w. Similar behavior is found for radiation efficiency (η_R). We use V_r^3Δσ_E and T_c/M_0^(1/3) to explore variation of stress drop, V_r and radiation efficiency, along with finite-source geometrical factors. Radiation efficiency tends to decrease with average slip for these very large events, and fracture Energy increases steadily with slip.
-
Representations of the Radiated Energy in Earthquakes
2004Co-Authors: Luis Rivera, Hiroo KanamoriAbstract:We investigate the representation of the Radiated Energy, E_R, in earthquakes. In seismology E_R is estimated from either far-field seismic waves or the stress and displacement on the fault plane. Although E_R comes from the entire volume of the Earth, it can be expressed as an integral over the fault plane. However, the integrand cannot be given a simple physical meaning such as the Radiated Energy density on the fault plane. The stress on the fault plane changes rapidly during a seismic rupture. Although the Energy Radiated by this process is not included in the estimate of E_R in a simplified practice in seismology, it is correctly included in the expression of E_R in standard seismological practice. Using the representation theorem, we can express E_R as a surface integral over the fault plane, with the integrand containing the slip function on the fault plane. However, the integrand at a point depends not only on the slip function at the point but also on the slip functions everywhere on the fault plane. Thus, the simple method in which E_R is estimated by summation of the local Energy flux on the fault plane does not yield a correct estimate.
-
Radiated Energy from the 16 october 1999 hector mine earthquake regional and teleseismic estimates
Bulletin of the Seismological Society of America, 2002Co-Authors: Anupama Venkataraman, Luis Rivera, Hiroo KanamoriAbstract:The amount of seismic Energy Radiated from an earthquake is a key macroscopic parameter for understanding the physics of earthquakes. To resolve the important details of the earthquake process, we require more accurate estimates of Energy than are currently available. In this study, we determine the Energy Radiated from the M_(w) 7.1 16 October 1999 Hector Mine, California, earthquake using regional data from 67 TriNet stations. Earlier estimates of Radiated Energy from regional data used empirical path and station attenuation corrections. Here, we remove the path and station attenuation effects by using an empirical Green's function deconvolution. We use one foreshock and four aftershocks as empirical Green's functions and determine the source spectra. The Radiated Energy at each of the regional stations is computed from these source spectra. The Energy estimates from the regional data are tightly clustered, with a mean estimate of 3.0 × 10^(15) J and a standard deviation of 0.9 × 1015 J. To calibrate the teleseismic methods currently used, we compare the Energy estimates obtained above with the Energy computed using two different teleseismic methods. The first method is based on the conventional National Earthquake Information Center (NEIC) method, in which the Energy flux at each station is computed by squaring and integrating the corrected velocity spectrum. In the second method, we compute Green's functions for the appropriate source structure and deconvolve these from the mainshock data to obtain the source spectrum at each station. The Energy is then calculated from the source spectra. The teleseismic Energy estimates have a mean of 1.8 × 10^(15) J and 2.0 × 10^(15) J for the two methods, respectively. The average estimate of Radiated Energy from teleseismic data is nearly the same as that obtained from the regional data (3 × 10^(15) J). From the mean Radiated Energy (3 × 10^(15) J) and moment (6 × 10^(19) N m) estimates, the Energy-to-moment ratio for the Hector Mine earthquake is 5 × 10^(–5).
Ru-zhou Luo - One of the best experts on this subject based on the ideXlab platform.
-
rock burst intensity classification based on the Radiated Energy with damage intensity at jinping ii hydropower station china
Rock Mechanics and Rock Engineering, 2015Co-Authors: Bing-rui Chen, Xia-ting Feng, Ru-zhou LuoAbstract:Based on the Radiated Energy of 133 rock bursts monitored by a microseismic technique at the Jinping II hydropower station, in Sichuan province, China, we analyzed the advantages and disadvantages of qualitative classification methods for the rock burst intensity. Then, we investigated the characteristics, magnitude, and laws of the Radiated Energy, as well as the relationship between the rock burst Radiated Energy and intensity. Then, we selected the Energy as an evaluation index for the rock burst intensity classification, and proposed a new rock burst intensity quantitative classification method, which utilized the hierarchical clustering analysis technique with the complete-linkage method. Next, we created a new set of criteria for the quantitative classification of the rock burst intensity based on Radiated Energy and surrounding rock damage severity. The new criteria classified the rock burst intensity into five levels: extremely intense, intense, moderate, weak, and none, and the common logarithms of the Radiated Energy of each level were >7 lg(E/J), >4 lg(E/J) and 2 lg(E/J) and 1 lg(E/J) and <2 lg(E/J), and <1 lg(E/J), respectively. Finally, we investigated the factors influencing the classification, and verified its feasibility and applicability via several practical rock burst examples.
-
Rock Burst Intensity Classification Based on the Radiated Energy with Damage Intensity at Jinping II Hydropower Station, China
Rock Mechanics and Rock Engineering, 2013Co-Authors: Bing-rui Chen, Xia-ting Feng, Li Qingpeng, Ru-zhou LuoAbstract:Based on the Radiated Energy of 133 rock bursts monitored by a microseismic technique at the Jinping II hydropower station, in Sichuan province, China, we analyzed the advantages and disadvantages of qualitative classification methods for the rock burst intensity. Then, we investigated the characteristics, magnitude, and laws of the Radiated Energy, as well as the relationship between the rock burst Radiated Energy and intensity. Then, we selected the Energy as an evaluation index for the rock burst intensity classification, and proposed a new rock burst intensity quantitative classification method, which utilized the hierarchical clustering analysis technique with the complete-linkage method. Next, we created a new set of criteria for the quantitative classification of the rock burst intensity based on Radiated Energy and surrounding rock damage severity. The new criteria classified the rock burst intensity into five levels: extremely intense, intense, moderate, weak, and none, and the common logarithms of the Radiated Energy of each level were >7 lg(E/J), >4 lg(E/J) and 2 lg(E/J) and 1 lg(E/J) and
Rebecca Joy Archuleta - One of the best experts on this subject based on the ideXlab platform.
-
Radiated seismic Energy based on dynamic rupture models of faulting
Journal of Geophysical Research, 2006Co-Authors: Shuo Ma, Rebecca Joy ArchuletaAbstract:[1] By modeling spontaneous ruptures, we study the mechanism dependence of Radiated seismic Energy from three hypothetical crustal events, 30° dipping reverse fault, 60° dipping normal fault, and a vertical strike-slip fault, and the 1994 blind-thrust Northridge earthquake. Embedded in a homogeneous half-space, all three hypothetical faults have the same area and are subjected to the same shear and normal stress conditions and frictional parameters. Dynamic simulations produce apparent stress of 0.53 MPa, 0.23 MPa, and 0.34 MPa for the reverse, normal, and strike-slip faults, respectively. The Energy distribution on a distant surface shows that a large fraction of Energy is concentrated in the forward direction of rupture propagation. We use spontaneous rupture models to compute the Radiated Energy from the 1994 Northridge earthquake. The initial stress drop distribution is based on a kinematic slip distribution. Using a linear slip-weakening friction law, we modify both the initial stress and yield stress until the dynamic rupture produces near-source synthetics that are consistent with the data. The total Radiated seismic Energy from our model is 6.0 × 1014 J; seismic moment 1.47 × 1019 Nm; apparent stress 1.5 MPa; fracture Energy 3.2 × 1014 J; and slip-weakening distance 0.25 m. The Energy flux distribution is heterogeneous with strong directivity effects. These results suggest that correcting for directivity could be difficult, but necessary, for teleseismic and regional estimates of Radiated Energy. Dynamic source models constrained by ground motions can provide a stable and accurate Energy estimate for large earthquakes.
-
Radiated seismic Energy based on dynamic rupture models of faulting
Journal of Geophysical Research, 2006Co-Authors: Shuo Ma, Rebecca Joy ArchuletaAbstract:[1] By modeling spontaneous ruptures, we study the mechanism dependence of Radiated seismic Energy from three hypothetical crustal events, 30° dipping reverse fault, 60° dipping normal fault, and a vertical strike-slip fault, and the 1994 blind-thrust Northridge earthquake. Embedded in a homogeneous half-space, all three hypothetical faults have the same area and are subjected to the same shear and normal stress conditions and frictional parameters. Dynamic simulations produce apparent stress of 0.53 MPa, 0.23 MPa, and 0.34 MPa for the reverse, normal, and strike-slip faults, respectively. The Energy distribution on a distant surface shows that a large fraction of Energy is concentrated in the forward direction of rupture propagation. We use spontaneous rupture models to compute the Radiated Energy from the 1994 Northridge earthquake. The initial stress drop distribution is based on a kinematic slip distribution. Using a linear slip-weakening friction law, we modify both the initial stress and yield stress until the dynamic rupture produces near-source synthetics that are consistent with the data. The total Radiated seismic Energy from our model is 6.0 × 1014 J; seismic moment 1.47 × 1019 Nm; apparent stress 1.5 MPa; fracture Energy 3.2 × 1014 J; and slip-weakening distance 0.25 m. The Energy flux distribution is heterogeneous with strong directivity effects. These results suggest that correcting for directivity could be difficult, but necessary, for teleseismic and regional estimates of Radiated Energy. Dynamic source models constrained by ground motions can provide a stable and accurate Energy estimate for large earthquakes.
