We mapped the minimum magnitude of complete reporting, M c , for Alaska, the western United States, and for the JUNEC earthquake catalog of Japan. Mc was estimated based on its departure from the linear frequency-magnitude relation of the 250 closest earthquakes to grid nodes, spaced 10 km apart. In all catalogs studied, Mc was strongly heterogeneous. In offshore areas the Mc was typically one unit of magnitude higher than onshore. On land also, Mc can vary by one order of magnitude over distance less than 50 km. We recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar Mc, or the minimum magnitude for the analysis has to be raised to the highest com- mon value of Mc. We believe that the data quality, as reflected by the Mc level, should be used to define the spatial extent of seismicity studies where Mc plays a role. The method we use calculates the goodness of fit between a power law fit to the data and the observed frequency-magnitude distribution as a function of a lower cutoff of the magnitude data. Mc is defined as the magnitude at which 90% of the data can be modeled by a power law fit. Mc in the 1990s is approximately 1.2 0.4 in most parts of California, 1.8 0.4 in most of Alaska (Aleutians and Panhandle excluded), and at a higher level in the JUNEC catalog for Japan. Various sources, such as ex- plosions and earthquake families beneath volcanoes, can lead to distributions that cannot be fit well by power laws. For the Hokkaido region we demonstrate how neglecting the spatial variability of M c can lead to erroneous assumptions about deviations from self-similarity of earthquake scaling.

http://basin.earth.ncu.edu.tw/download/courses/seminar_MSc/2009/0225-2_Minimum%20Magnitude%20of%20Completeness%20in%20Earthquake%20Catalogs-%20Examples%20from%20Alaska,%20the%20Western%20United%20States,%20and%20Japan.pdf

Minimum Magnitude of Completeness in Earthquake Catalogs: Examples from Alaska, the Western United States, and Japan

The Electronic Seismologist (ES) has been known to actually do some research in the field of seismology from time to time. As an operator of a seismic monitoring network the research done often is related to the seismicity of the monitored region. Detecting changes or trends in seismicity is relevant to earthquake and volcano hazards, but are the trends detected real or only an artifact of changes in the network operating parameters? Because all seismic networks evolve, change staff, change software and hardware, there is always the nagging feeling, if not outright knowledge, that interesting patterns in the catalog reflect network changes rather than changes in the Earth. How can one tell the difference?

The ES is happy to report that there is a handy-dandy software package ideally suited to answering exactly this question (and many others). ZMAP , developed by Stefan Wiemer, allows the user to examine an earthquake catalog from many different angles. Not only does it include the traditional map, cross-section, and time sequence parameters, but also several others, such as event size and mechanism. These can be combined in interesting ways to present the user with different “views” into the data. Considerable seismological acumen lies behind the use and presentation of these parameters, which helps the user get the most out of the analyzed catalog. ZMAP is fairly intuitive to use and produces attractive output. In fact, the ES actually has fun “playing” with it and gets useful results besides. Perhaps one of the best ways to get a sense of how ZMAP might be used is to take a tour of case studies. The following includes many examples, and if they're not enough there are a slew of references where one can find more. In his traditional groveling way the ES has prevailed on Stefan …

A Software Package to Analyze Seismicity: ZMAP

We introduce a new method to determine the magnitude of complete- ness Mc and its uncertainty. Our method models the entire magnitude range (EMR method) consisting of the self-similar complete part of the frequency-magnitude dis- tribution and the incomplete portion, thus providing a comprehensive seismicity model. We compare the EMR method with three existing techniques, finding that EMR shows a superior performance when applied to synthetic test cases or real data from regional and global earthquake catalogues. This method, however, is also the most computationally intensive. Accurate knowledge of Mc is essential for many seismicity-based studies, and particularly for mapping out seismicity parameters such as the b-value of the Gutenberg-Richter relationship. By explicitly computing the uncertainties in Mc using a bootstrap approach, we show that uncertainties inb-values are larger than traditionally assumed, especially when considering small sample sizes. As examples, we investigated temporal variations of Mc for the 1992 Landers aftershock sequence and found that it was underestimated on average by 0.2 with former techniques. Mapping Mc on a global scale, Mc reveals considerable spatial variations for the Harvard Centroid Moment Tensor (CMT) (5.3 Mc 6.0) and the International Seismological Centre (ISC) catalogue (4.3 Mc 5.0).

Assessing the Quality of Earthquake Catalogues: Estimating the Magnitude of Completeness and Its Uncertainty

SUMMARY In this paper we present a global model (GSRM-1) of both horizontal velocities on the Earth’s surface and horizontal strain rates for almost all deforming plate boundary zones. A model strain rate field is obtained jointly with a global velocity field in the process of solving for a global velocity gradient tensor field. In our model we perform a least-squares fit between model velocities and observed geodetic velocities, as well as between model strain rates and observed geological strain rates. Model velocities and strain rates are interpolated over a spherical Earth using bi-cubic Bessel splines. We include 3000 geodetic velocities from 50 different, mostly published, studies. Geological strain rates are obtained for central Asia only and they are inferred from Quaternary fault slip rates. For all areas where no geological information is included a priori constraints are placed on the style and direction (but not magnitude) of the model strain rate field. These constraints are taken from a seismic strain rate field inferred from (normalized) focal mechanisms of shallow earthquakes. We present a global solution of the second invariant of the model strain rate field as well as strain rate solutions for a few selected plate boundary zones. Generally, the strain rate tensor field is consistent with geological and seismological data. With the assumption of plate rigidity for all areas other than the plate boundary zones we also present relative angular velocities for most plate pairs. We find that in general there is a good agreement between the present-day plate motions we obtain and longterm plate motions, but a few significant differences exist. The rotation rates for the Indian, Arabian and Nubian plates relative to Eurasia are 30, 13 and 50 per cent slower than the NUVEL1A estimate, respectively, and the rotation rate for the Nazca Plate relative to South America is 17 per cent slower. On the other hand, Caribbean‐North America motion is 76 per cent faster than the NUVEL-1A estimate. While crustal blocks in the India‐Eurasia collision zone move significantly and self-consistently with respect to bounding plates, only a very small motion is predicted between the Nubian and Somalian plates. By integrating plate boundary zone deformation with the traditional modelling of angular velocities of rigid plates we have obtained a model that has already been proven valuable in, for instance, redefining a no-net-rotation model of surface motions and by confirming a global correlation between seismicity rates and tectonic moment rates along subduction zones and within zones of continental deformation.

/pdf/an-integrated-global-model-of-present-day-plate-motions-and-57ic0m6oev.pdf

An integrated global model of present-day plate motions and plate boundary deformation

http://home.ustc.edu.cn/~ly2014/Advances_in_Geosciences/Reading%20materials%20for%20Week%202/Group6-Characterisation%20of%20the%20Basel%201%20enhanced%20geothermal%20system.pdf

Characterisation of the Basel 1 enhanced geothermal system

An automatic detection algorithm has been developed which is capable of time P -phase arrivals of both local and teleseismic earthquakes, but rejects noise bursts and transient events. For each signal trace, the envelope function is calculated and passed through a nonlinear amplifier. The resulting signal is then subjected to a statistical analysis to yield arrival time, first motion, and a measure of reliability to be placed on the P -arrival pick. An incorporated dynamic threshold lets the algorithm become very sensitive; thus, even weak signals are timed precisely. During an extended performance evaluation on a data set comprising 789 P phases of local events and 1857 P phases of teleseismic events picked by an analyst, the automatic picker selected 66 per cent of the local phases and 90 per cent of the teleseismic phases. The accuracy of the automatic picks was “ideal” (i.e., could not be improved by the analyst) for 60 per cent of the local events and 63 per cent of the teleseismic events.

An automatic phase picker for local and teleseismic events

[1] We present a new approach to determine precise and reliable hypocenter locations in the tectonically complex region of Switzerland. A three-dimensional (3-D) P wave velocity model to be used for earthquake relocation is obtained by simultaneously inverting arrival times of local earthquakes for hypocenter locations and 3-D P wave velocity structure. A 3-D P wave velocity model derived from controlled source seismology (CSS) is used as an initial reference model. The final 3-D model thus combines all available information from both CSS and local earthquake data. The probabilistic, nonlinear formulation of the earthquake location problem includes a complete description of location uncertainties and can be used with any kind of velocity model. In particular, the combination of nonlinear, global search algorithms, such as the Oct-Tree Importance Sampling, with probabilistic earthquake location provides a fast and reliable tool for earthquake location. The comparison of hypocenter locations obtained routinely by the Swiss Seismological Service (SED) to those relocated in the new 3-D velocity model using a probabilistic approach reveals no systematic shifts but does exhibit large individual shifts in some epicenter locations and focal depths. We can attribute these large shifts in part to large uncertainties in the hypocenter location. Events with a low number of observations (<8) and no observation within the critical focal depth distance typically show large location uncertainties. Improved hypocentral locations, particularly for mine blasts and earthquakes whose routine hypocenter locations had been questionable, confirm that improved velocity model and probabilistic earthquake location yield more precise and reliable hypocenter locations and associated location uncertainties for Switzerland.

Probabilistic earthquake location in complex three‐dimensional velocity models: Application to Switzerland

Earthquakes in Switzerland and Surrounding Regions During 1999

Regional moment tensor determination in the European–Mediterranean area — initial results

We present an algorithm to identify and remove quarry explosions from earthquake catalogs while retaining a maximum amount of data. For most seismicity studies, quarry blasts are a data contamination that obscures natural phenomena under investigation. Based on the fact that most quarry blasts are performed during daytime hours, we spatially map out the ratio of daytime to nighttime events, Rq. This type of map clearly identifies regions of high quarry activity. A grid search identifies the highest Rq volume, which is subsequently removed from the data. This process is repeated until no volume with an anomalous ratio of daytime to nighttime events with significance greater than 99% remains. Examples for Switzerland, Alaska, and the western United States demonstrate the capabilities of the algorithm, where the algorithm removes 20%, 6%, and 0.75% of the events, respectively. We suggest that computing maps of Rq should be a routine part of any microseismicity study

Manuscript received 21 July 1999.

Manfred Baer

Papers

An automatic phase picker for local and teleseismic events

Probabilistic earthquake location in complex three‐dimensional velocity models: Application to Switzerland

Earthquakes in Switzerland and Surrounding Regions During 1999

Regional moment tensor determination in the European–Mediterranean area — initial results

Mapping and Removing Quarry Blast Events from Seismicity Catalogs