Application of conditional geostatistical simulation to calculate the probability of occurrence of earthquakes belonging to a seismic series

Geostatistics offers various techniques of estimation and simulation that have been satisfactorily applied in solving geological problems. In this sense, conditional geostatistical simulation is applied to calculate the probability of occurrence of an earthquake with a lower than or equal magnitude to one determined during a seismic series. It is possible to calculate the energy of the next most probable earthquake from a specific time, given knowledge of the structure existing among earthquakes occurring prior to a specific moment.     

A test of the precursory accelerating moment release model on some recent New Zealand earthquakes

The proposal that the moment release rate increases in a systematic way in a large region around a forthcoming large earthquake is tested using three recent, large New Zealand events. The three events, 1993–1995, magnitudes 6.7–7.0, occurred in varied tectonic settings. For all three events, a circular precursory region can be found such that the moment release rate of the included seismicity is modelled significantly better by the proposed accelerating model than by a linear moment release model, although in one case the result is dubious. The 'best' such regions have radii from 122 to 167 km, roughly in accord with previous observations world-wide, but are offset by 50–60 km from the associated main shock epicentre. A grid-search procedure is used to test whether these three earthquakes could have been forecast using the accelerating moment release model. For two of the earthquakes the result is positive in terms of location, but the main shock times are only loosely constrained.     

Method for UAV-based 3D topography reconstruction of tidal creeks

It is common to obtain the topography of tidal flats by the Unmanned Aerial Vehicle(UAV) photogrammetry,but this method is not applicable in tidal creeks.The residual water will lead to inaccurate depth inversion results,and the topography of tidal creeks mainly de-pends on manual survey.The present study took the tidal creek of Chuandong port in Jiangsu Province,China,as the research area and used UAV oblique photogrammetry to reconstruct the topography of the exposed part above the water after the ebb tide.It also proposed a Trend Prediction Fitting (TPF) method for the topography of the unexposed part below the water to obtain a complete 3D topography.The topography above the water measured by UAV has the vertical precision of 12 cm.When the TPF method is used,the cross-section should be perpendicular the central axis of the tidal creek.A polynomial function can be adapted to most shape of sections,while a Fourier function obtains better results in asym-metrical sections.Compared with the two-order function,the three-order function lends itself to more complex sections.Generally,the TPF method is more suitable for small,straight tidal creeks with clear texture and no vegetation cover.     

白令海峡及其邻近海域潮汐潮能数值模拟

基于非结构三角形网格的FVCOM(Finite-Volume Coastal Ocean Model)海洋数值模式,对白令海峡及其邻近海域的潮汐、潮能进行数值模拟研究。模拟结果同验潮站和实测海流资料符合良好,较好地反映了白令海峡及其邻近海域的潮汐、潮流分布特征和运动状况。根据计算结果绘制了主要分潮的同潮图和潮流椭圆图,对该海域潮汐潮流特征进行了系统分析。结果表明,白令海陆架区、白令海峡和楚科奇海主要以M2分潮为主,而在诺顿湾海域以K1分潮为主,M2分潮潮流在白令海陆架东南部及阿纳德尔湾较强,K1分潮潮流在诺顿湾潮流达到最大值。在此基础上,对其潮汐能的传播与耗散进行分析,结果发现研究海域潮能通量较小,主要分潮在研究海域潮能耗散总量约为751 MW,M2潮能耗散占该总量的52%,K1潮能耗散占38%,潮能进入白令海陆架后,M2分潮主要在圣劳伦斯岛以南陆架区耗散,K1分潮主要在诺顿湾海区耗散。     

A note on the surface volume change of shallow earthquakes

Summary. This note presents an exact analytical formula for determining the magnitude of coseismic surface volume change (δ V ) of earthquake faults in a half-space. For a Poisson solid, the formula is remarkably simple; δ V = M _zz |8μ, where M _zz is one of the moment tensor elements of the source. Maximum δ V values derive from dip slip on faults plunging 45°. For these events, surface volume changes of 0.0001 and 4.3 km³ can be expected for magnitude 5 and 8 earthquakes respectively. All of the coseismic surface volume change is recovered in the interseismic period through relaxation of the Earth and rebound of the surface. A useful rule of thumb for estimating the magnitude of vertical rebound in 45° dip slip events is δ h _p=Δ s /24, where Δ s is the coseismic slip on the fault.     

Applicability of time-to-failure analysis to accelerated strain before earthquakes and volcanic eruptions

We examine quantitatively the ranges of applicability of the equation Ω= A+B [1− t/t _f ] ^m for predicting 'system-sized' failure times t _f in the Earth. In applications Ω is a proxy measure for strain or crack length, and A , B and the index m are model parameters determined by curve fitting. We consider constitutive rules derived from (a) Charles' law for subcritical crack growth; (b) Voight's equation; and (c) a simple percolation model, and show in each case that this equation holds only when m < 0. When m > 0, the general solution takes the form Ω = A + B [1 + t / T  ] ^m , where T   is a positive time constant, and no failure time can be defined. Reported values for volcanic precursors based on rate data are found to be within the range of applicability of time-to-failure analysis ( m < 0). The same applies to seismic moment release before earthquakes, at the expense of poor retrospective predictability of the time of the a posteriori -defined main shock. In contrast, reported values based on increasing cumulative Benioff strain occur in the region where a system-sized failure time cannot be defined ( m > 0; commonly m ≈ 0.3). We conclude on physical grounds that cumulative seismic moment is preferred as the most direct measure of seismic strain. If cumulative Benioff strain is to be retained on empirical grounds, then it is important that these data either be re-examined with the independent constraint m < 0, or that for the case 0 < m + 1 < 1, a specific correction for the time-integration of cumulative data be applied, of the form ΣΩ = At + B '{1 − [1 − t/t _f ] ^m+1 }.     

The relationship between seismic deformation and deep-seated gravitational movements during the 1997 Umbria–Marche (Central Italy) earthquakes

This paper re-evaluates the origin of some peculiar patterns of ground deformation in the Central Apennines, observed by space geodetic techniques during the two earthquakes of the Colfiorito seismic sequence on September 26th, 1997. The surface displacement field due to the fault dislocation, as modelled with the classic Okada elastic formulations, shows some areas with high residuals which cannot be attributed to non-simulated model complexities. The residuals were investigated using geomorphological analysis, recognising the geologic evidence of deep-seated gravitational slope deformations (DSGSD) of the block-slide type. The shape and direction of the co-seismic ground displacement observed in these areas are correlated with the expected pattern of movement produced by the reactivation of the identified DSGSD. At least a few centimetres of negative “Line of Sight” ground displacement was determined for the Costa Picchio, Mt. Pennino, and Mt. Prefoglio areas. A considerable horizontal component of movement in the Costa Picchio DSGSD is evident from a qualitative analysis of ascending and descending interferograms. The timing of the geodetic data indicates that the ground movement occurred during the seismic shaking, and that it did not progress appreciably during the following months. This work has verified the seismic triggering of DSGSD previously hypothesized by many researchers. A further implication is that in the assessment of DSGSD hazard seismic input needs to be considered as an important cause of accelerated deformation.