On the relation between point-wise and multiple-location probabilistic seismic hazard assessments     

Vladimir Sokolov  Friedemann Wenzel 《Bulletin of Earthquake Engineering》2015,13(5):1281-1301

  相似文献   

On the use of JMA intensity in earthquake early warning systems     

Vladimir Sokolov  Takashi Furumura  Friedemann Wenzel 《Bulletin of Earthquake Engineering》2010,8(4):767-786

The estimation of strength of shaking at a site from the initial P-wave portion of ground motion is the key problems for shortening the alert time of the earthquake Early Warning (EEW). The most of the techniques proposed for the purpose utilize (a) ground motion models based on the estimated magnitude and hypocentral distance, or (b) the interim proxies, such as initial vertical displacement P _d . We suggest the instrumental Japan Meteorological Agency (JMA) intensity (JMA_I) as a characteristic for fast estimation of damage potential in the EEW systems. We investigated the scaling relations between JMA_I measured using the whole earthquake recordings (overall intensity) and using particular time intervals of various duration (2.0–8.0 s) starting from the P-wave arrival (preliminary intensity). The dataset included 3,660 records (K-NET and the KiK-net networks) from 55 events (M _W 4.1–7.4) occurred in 1999–2008 in Japan. We showed that the time interval of 4–5 s from the P-wave arrival can be used for reliable estimations of the overall intensity with the average standard error of about 0.5 JMA units. The uncertainty in the prediction may be reduced by consideration of local site conditions or by development of the station-specific models.  相似文献   

Probability of earthquake occurrence and magnitude estimation in the post shut-in phase of geothermal projects   总被引：1，自引：1，他引：0  

Andreas Barth  Friedemann Wenzel  Cornelius Langenbruch 《Journal of Seismology》2013,17(1):5-11

Induced seismicity in geothermal projects is observed to continue after shut-in of the fluid injection. Recent experiments show that the largest events tend to occur after the termination of injection. We use a probabilistic approach based on Omori??s law and the Gutenberg?CRichter magnitude?Cfrequency distribution to demonstrate that the probability of exceeding a certain maximum magnitude still increases after shut-in. This increase is governed by the exponent of Omori??s law q and the Gutenberg?CRichter b value. For a reduced b value in the post-injection phase, the probability of occurrence directly after shut-in can be even higher than the corresponding probability for an ongoing injection. For the reference case of q?=?2 and a 10% probability at shut-in time t _S to exceed a given maximum magnitude, we obtain an increase to 14.6% for t?=?2t _S at a constant Gutenberg?CRichter b value after shut-in. A reduction of the b value by one quarter leads to a probability of 20.5%. If we consider a constant probability level of occurrence for an event larger than a given magnitude at shut-in time, this maximum magnitude increases by 0.12?units for t?=?2t _S (0.26?units for a reduced b value). For the Soultz-sous-Forêts (France) injection experiment in 2000, recent studies reveal q?=?9.5 and a b value reduction by 14%. A magnitude 2.3 event 9?h after shut-in falls in the phase with a probability higher than for the continued injection. The probability of exceeding the magnitude of this post-injection event is determined to 97.1%.  相似文献   

Earthquake forewarning — A multidisciplinary challenge from the ground up to space     

Friedemann Freund 《Acta Geophysica》2013,61(4):775-807

Most destructive earthquakes nucleate at between 5–7 km and about 35–40 km depth. Before earthquakes, rocks are subjected to increasing stress. Not every stress increase leads to rupture. To understand pre-earthquake phenomena we note that igneous and high-grade metamorphic rocks contain defects which, upon stressing, release defect electrons in the oxygen anion sublattice, known as positive holes. These charge carriers are highly mobile, able to flow out of stressed rocks into surrounding unstressed rocks. They form electric currents, which emit electromagnetic radiation, sometimes in pulses, sometimes sustained. The arrival of positive holes at the ground-air interface can lead to air ionization, often exclusively positive. Ionized air rising upward can lead to cloud condensation. The upward flow of positive ions can lead to instabilities in the mesosphere, to mesospheric lightning, to changes in the Total Electron Content (TEC) at the lower edge of the ionosphere, and electric field turbulences. Advances in deciphering the earthquake process can only be achieved in a broadly multidisciplinary spirit.  相似文献   

Potential of Earthquake Early Warning Systems   总被引：2，自引：0，他引：2  

Wenzel  Friedemann  Baur  Michael  Fiedrich  Frank  Ionescu  Constantin  Ionescu  Mihnea C. 《Natural Hazards》2001,23(2-3):407-416

Despite their short warning times (seconds to tens of seconds)earthquake early warning systems can become useful tools in riskmitigation provided their design is robust and utilizes theregional tectonics. Bucharest can serve as a good example forsuch a system with a warning time of 25 seconds. Integration ofearly warning into real-time information systems turns out beingcrucial in disaster management.  相似文献   

Hydrostatic pressure tests for the permeability - formation factor relation on crystalline rocks from the KTB drilling project     

Dieter Freund  Georg Nover 《Surveys in Geophysics》1995,16(1):47-62

Transport properties (permeability and electrical conductivity) have been measured at different hydrostatic pressure runs on 7 crystalline rocks (gneisses and amphibolites) sampled from the KTB drilling project. The decrease of permeability by pressure are compared with the pressure-dependent data of the electrical conductivity (formation factor) resulting from complex impedance measurements. According to the equivalent-channel model (ECM), there exists a linear relationship between these parameters by representing both properties on logarithmic scales. The results show that it is possible to extrapolate high-pressure permeability from low-pressure (< 60 MPa) permeability data by using the pressure-dependent electrical conductivity (up to 300 MPa).  相似文献   

Mechanism of the water and carbon dioxide solubility in oxides and silicates and the role of O−     

Friedemann Freund 《Contributions to Mineralogy and Petrology》1981,76(4):474-482

The dissolution of water does not stop at the OH^– stage but may proceed further towards H₂ plus O^– formation. The discovery of atomic carbon dissolved in minerals suggests that, if CO₂ enters oxides and silicates at high pressures and temperatures, not only [CO₃]^2– ions but also [CO ₄ ^. ]^4– complexes are formed via a charge transfer which produces O^– and essentially zero-valent, atomic carbon. Under P —T-conditions of the mantle, where the solubility for water and CO₂ is high, the silicate phases formed may therefore consist to a large volume fraction of O^– ions which are much smaller than O^2–ions and strongly cova-lently bonding. The implications for the crystal chemistry of high pressure phases, for the petrology of mantle rocks are outlined.  相似文献   

Carbon in solid solution in forsterite—a key to the untractable nature of reduced carbon in terrestrial and cosmogenic rocks     

F. Freund  H. Kathrein  H. Wengeler  R. Knobel  H.J. Reinen 《Geochimica et cosmochimica acta》1980,44(9):1319-1333

Carbon is an incompatible element in oxide and silicate lattices. Until now it has been believed to exist only in the form of CO^2?₃ ions, molecularily dissolved CO₂ or graphitic inclusions. Recently it has been shown that carbon can dissolve in refractory oxides, like MgO and CaO, in the form of carbon atoms.The experimental results obtained with carbonaceous MgO are reviewed and new results are presented which demonstrate that synthetic forsterite and natural olivines can also take up atomic carbon in solid solution. The incorporation of the carbon atoms is treated thermodynamically. Near the melting point they probably occupy cation vacancies, but with decreasing temperature they are progressively transferred on interstitial sites. On these sites they are very mobile and tend to segregate into the elastically relaxed subsurface zone, but exsolution to graphite is prevented by the strain fields surrounding each carbon atom.Upon heating, however, the atomic carbon may react with lattice oxygen to give CO₂ and with co-dissolved hydrogen to give a wide variety of hydrocarbons. The underlying reaction mechanisms, involving the formation and decay of O^? ions, are discussed in view of the so-called ‘carbonatic carbon’ and ‘reduced carbon’ in magmatic minerals and meteorites, in view of the diamond genesis and also in view of the reversible CO₂ solubility in silicate magmas at high pressures and temperatures.  相似文献   

Accounting for site effect in probabilistic assessment of seismic hazard for Romania and Bucharest: a case of deep seismicity in Vrancea zone     

Vladimir Sokolov  Klaus-Peter Bonjer  Friedemann Wenzel 《Soil Dynamics and Earthquake Engineering》2004,24(12):929-947

The paper presents recent achievements in evaluations of site-dependent seismic hazard in Romania and the capital city of Bucharest caused by the Vrancea focal zone (SE-Carpathians). The zone is characterized by a high rate of occurrence of large earthquakes in a narrow focal volume at depths 60–170 km. The database that was used for the hazard evaluation includes parameters of seismicity, ground-motion source scaling and attenuation models (Fourier amplitude spectra), and site-dependent spectral amplification functions. Ground-motion characteristics were evaluated on the basis of several hundred records from more than 120 small magnitude (M 3.5–5) earthquakes occurred in 1996–2001 and a few tens of acceleration records obtained during four large (M 7.4, 7.2, 6.9 and 6.3) earthquakes. The data provide a basis for probabilistic seismic hazard assessment in terms of peak ground acceleration, peak spectral acceleration and MSK intensity using Fourier amplitude spectra for various exceedance probabilities or average return periods. It has been shown that the influence of geological factors plays very important role in distribution of earthquake ground-motion parameters along the territory of Romania.  相似文献   

Charge generation and propagation in igneous rocks   总被引：5，自引：0，他引：5  

Friedemann Freund   《Journal of Geodynamics》2002,33(4-5)

Various electrical phenomena have been reported prior to or concurrent with earthquakes such as resistivity changes, ground potentials, electromagnetic (EM), and luminous signals. Doubts have been raised as to whether some of these phenomena are real and indeed precursory. One of the reasons for uncertainty is that, despite decades of intense work, there is still no physically coherent model. Using low- to medium-velocity impacts to measure electrical signals with microsecond time resolution, it has now been observed that when dry gabbro and diorite cores are impacted at relatively low velocities, 100 m/s, highly mobile charge carriers are generated in a small volume near the impact point. They spread through the rocks, causing electric potentials exceeding +400 mV, EM, and light emission. As the charge cloud spreads, the rock becomes momentarily conductive. When a dry granite block is impacted at higher velocity, 1.5 km/s, the propagation of the P and S waves is registered through the transient piezoelectric response of quartz. After the sound waves have passed, the surface of the granite block becomes positively charged, suggesting the same charge carriers as observed during the low-velocity impact experiments, expanding from within the bulk. During the next 2–3 ms the surface potential oscillates, indicating pulses of electrons injected from ground and contact electrodes. The observations are consistent with positive holes, e.g. defect electrons in the O²⁻ sublattice, traveling via the O 2p-dominated valence band of the silicate minerals. Before activation, the positive holes lay dormant in the form of electrically inactive positive hole pairs (PHP), chemically equivalent to peroxy links, O₃X/^OO\XO₃, with X=Si⁴⁺, Al³⁺, etc. PHPs are introduced into the minerals by way of hydroxyl, O₃X–OH, which all nominally anhydrous minerals incorporate when crystallizing in H₂O-laden environments. The fact that positive holes can be activated by low-energy impacts, and their attendant sound waves, suggests that they can also be activated by microfracturing. Depending on where in the stressed rock volume the charge carriers are activated, they will form rapidly moving or fluctuating charge clouds that may account for earthquake-related electrical signals and EM emission. Wherever such charge clouds intersect the surface, high fields are expected, causing electric discharges and earthquake lights.  相似文献