Depth variation of seismic moment and recurrence interval in Japan

In repeating seismic event sequences within a specialized horizontal area, the moment magnitude is usually scaled with the recurrence interval. In addition to two horizontal dimensions, the vertical dimension plays a certain role in affecting the scaling law. However, whether and how the changing depth influences the scaling law remain enigmatic. Based on a large number of earthquake records with high-resolution epicenter locations in recent decades in Japan, we focus on a comparison between the 3-D seismic moment and seismic interval, which recognize the vertical dimension as the same dimension as the horizontal distances. The results show that (1) the seismic moment scaling law is applicable in the multiparameter 3-D models by visiting the 1.8 million events collected during a period of 15 years; (2) the vertical dimension of depth plays an important role in the Mo–SI relationship as well as in the variance in the 3-D seismic moment–interval magnitudes; and (3) the seismic moment rate, attributable to the plate convergence rate, varies with area and depth in influencing the regional earthquake recurrence frequency.

The slip deficit along the North Anatolian Fault (Turkey) in the Marmara Sea: Insights from paleoseismicity, seismicity and geodetic data

<p>The North Anatolian Fault experienced large earthquakes with 250 to 400 years recurrence time. In the Marmara Sea region the 1999 (Mw = 7.4) and the 1912 (Mw = 7.4) earthquake ruptures bound the Central Marmara Sea fault segment. Using historical-instrumental catalogue and paleoseismic results (≃ 2000-year database), the mapped fault segments, fault kinematic and GPS data, we compute the paleoseismic-seismic moment rate and geodetic moment rate. The geodetic moment rate is obtained by projecting the measured surface displacements to estimate the strain rate, and evaluating the associated elastic stress rate over a regular spatial grid. The paleoseismic-seismic moment rate is obtained by summing the moment tensors over regions of the spatial grid and periods of time. A clear discrepancy appears between the moment rates and implies a significant delay in the seismic slip along the fault. The rich database allows us to identify the size of the seismic gap and related fault segment and estimate the moment rate deficit. Our modeling suggest that the locked Central Marmara Sea fault segment even including a creeping section bears a moment rate deficit  = 6.4*10<sup>17</sup> N.m./yr. that corresponds to Mw ≃ 7.4 for a future earthquake with an average ≃ 3.25 m coseismic slip. Taking into account the uncertainty in the strain accumulation along the 130-km-long Central fault segment, our estimate of the seismic slip deficit being ≃ 10 mm/yr implies the size of the future earthquake ranges between Mw = 7.4 and 7.5.</p>

THE CONTRIBUTION OF EARTHQUAKES TO THE DEFORMATION OF ZAGROS TECTONIC PROVINCE

In this study, we investigate the contribution of earthquakes to the deformation of Zagros province and compare the seismicity and the density of earthquakes in different parts of the province. The mathematics used in this research is based on calculations of moment rates. The seismic moment rate is the average amount of seismic energy releases from the tectonic province in each year. The geodetic moment rate is the average amount of energy which is consumed every year to make deformation in Zagros. The ratio of these two moment rates expresses the contribution of earthquakes in making deformation in Zagros province. According to the calculations, this ratio is estimated to be 13.06%. Along with the information obtained from the moment rates, we can also obtain the shear and the dilative strain rates from the strain rate tensors, which show the volumetric changes and the deformation rate in different parts of the Zagros, respectively. The data used in this study include the focal coordinates of the Zagros earthquakes with their magnitude and the velocity vectors of the Zagros geodynamic network, which are used to calculate the seismic and the geodetic moment rates.

Maximum magnitude of subduction earthquakes along the Japan-Kuril-Kamchatka trench estimated from seismic moment conservation

SUMMARY We estimated the maximum magnitude of earthquakes in the Japan-Kuril-Kamchatka trench subduction zone with a method based on the conservation of seismic moment and the record of interplate seismicity from 1977 to 2017. The key point of this method is to base calculations on the tectonic moment rate instead of the total seismic moment rate. We modeled a seismic-moment-frequency distribution for the Japan-Kuril-Kamchatka trench on the basis of the truncated Gutenberg–Richter (G–R) law, the formula published by Utsu in 1974, the gamma distribution, and the tapered G–R law. We estimated the maximum magnitude along the Japan-Kuril-Kamchatka trench as ∼10 under the truncated G–R law and ∼11 under Utsu's formula, although the latter may be an overestimate. Therefore, the 2011 Tohoku earthquake, of moment magnitude 9.2, may not be the largest possible event in this area. The recurrence interval for magnitude 10 events based on the truncated G–R law is 4000 yr. Although these two models perform equally well in terms of Akaike Information Criterion, the range of the 95 per cent confidence level is consistently narrower for the truncated G–R law than for Utsu's formula. The estimated maximum magnitude depends not only on the model used, but also on the parameters that constitute the tectonic moment. It is essential to accumulate more seismic data and achieve more precise estimates of tectonic moment to improve estimates of maximum magnitude.

Some preliminary results of a worldwide seismicity estimation: a case study of seismic hazard evaluation in South America

Global data have been widely used for seismicity and seismic hazard assessment by seismologists. In the present study we evaluate worldwide seismicity in terms of maps of maximum observed magnitude (Mmax), seismic moment (M 0 ) and seismic moment rate (M 0S). The data set used consists of a complete and homogeneous global catalogue of shallow (h £ 60 km) earthquakes of magnitude MS ³ 5.5 for the time period 1894-1992. In order to construct maps of seismicity and seismic hazard the parameters a and b derived from the magnitude-frequency relationship were estimated by both: a) the least squares, and b) the maximum likelihood, methods. The values of a and b were determined considering circles centered at each grid point 1° (of a mesh 1° ´1°) and of varying radius, which starts from 30 km and moves with a step of 10 km. Only a and b values which fulfill some predefined conditions were considered in the further procedure for evaluating the seismic hazard maps. The obtained worldwide M max distribution in general delineates the contours of the plate boundaries. The highest values of M max observed are along the circum-Pacific belt and in the Himalayan area. The subduction plate boundaries are characterized by the largest amount of M 0 , while areas of continental collision are next. The highest values of seismic moment rate (per 1 year and per equal area of 10 000 km 2) are found in the Southern Himalayas. The western coasts of U.S.A., Northwestern Canada and Alaska, the Indian Ocean and the eastern rift of Africa are characterized by high values of M 0 , while most of the Pacific subduction zones have lower values of seismic moment rate. Finally we analyzed the seismic hazard in South America comparing the predicted by the NUVEL1 model convergence slip rate between Nazca and South America plates with the average slip rate due to earthquakes. This consideration allows for distinguishing between zones of high and low coupling along the studied convergence plate boundary.

A mutually consistent seismic-hazard source model for southern California

A previous attempt to integrate geological, geodetic, and observed seismicity data into a probabilistic-hazard source model predicted a rate of magnitude 6 to 7 earthquakes significantly greater than that observed historically. One explanation was that the discrepancy, or apparent earthquake deficit, is an artifact of the upper magnitude limit built into the model. This was controversial, however, because removing the discrepancy required earthquakes larger than are seen in the geological record and larger than implied from empirical relationships between fault dimension and magnitude. Although several articles have addressed this issue, an alternative, integrated source model without an apparent deficit has not yet appeared. We present a simple geologically based approach for constructing such a model that agrees well with the historical record and does not invoke any unsubstantiated phenomena. The following factors are found to be influential: the b-value and minimum magnitude applied to Gutenberg-Richter seismicity; the percentage of moment released in characteristic earthquakes; a round-off error in the moment-magnitude definition; bias due to historical catalog incompleteness; careful adherence to the conservation of seismic moment rate; uncertainty in magnitude estimates obtained from empirical regressions; allowing multi-segment ruptures (cascades); and the time dependence of recurrence rates. The previous apparent deficit is shown to have resulted from a combination of these factors. None alone caused the problem nor solves it. The model presented here is relatively robust with respect to these factors.