Production of a homogeneous seismic catalog based on machine learning for northeast Egypt

This research presents a new approach which addresses the conversion of earthquake magnitude as a supervised machine-learning problem through a multistage approach. First, the moment magnitude (M w) calculations were extended to lower magnitude earthquakes using the spectral P-wave analyses of the vertical component seismograms to improve the scaling relation of M w and the local magnitude (M L) of 138 earthquakes in northeastern Egypt. Second, using unsupervised clustering and regression analysis, we applied the k-means clustering technique to subdivide the mapped area into multiple seismic activity zones. This clustering phase created five spatially close seismic areas for training regression algorithms. Supervised regression analysis of each seismic area was simpler and more accurate. Conversion relations between M w and M L were calculated by linear regression, general orthogonal regression (GOR), and random sample consensus (RANSAC) regression techniques. RANSAC and GOR produced better results than linear regression, which provides evidence for the effects of outliers on regression accuracy. Moreover, the overall multistage hybrid approach produced substantial improvements in the measured-predicted dataset residuals when individual seismic zones rather than all datasets were considered. In 90% of the analyzed cases, M w values could be regarded as M L values within 0.2 magnitude units. Moreover, predicted magnitude conversion relations in the current study corresponded well to magnitude conversion relations in other seismogenic areas of Egypt.

Regional Earthquake Magnitude Conversion Relations for the Himalayan Seismic Belt

We present regional earthquake magnitude conversion relations among different magnitude scales (Mw, Ms, mb, ML, and MD) for the Himalayan seismic belt developed from data of local, regional, and international seismological agencies (International Seismological Centre [ISC], National Earthquake Information Centre [NEIC], Global Centroid Moment Tensor Solution [CMT], International Data Centre [IDC], China Earthquake Administration [BJI], and National Centre for Seismology [NDI]). The intra- (within the same magnitude scale) and inter- (with different magnitude scales) magnitude regression relations have been established using the general orthogonal regression and orthogonal distance regression techniques. Results show that the intra-magnitude relations for Mw, Ms, and mb reported by the Global CMT, ISC, and NEIC exhibit 1:1 relationships, whereas ML reported by the IDC, BJI, and NDI deviates from this relationship. The IDC underestimates Ms and mb compared with the ISC, NEIC, and Global CMT; this may be due to different measurement procedures adopted by the IDC agency. The inter-magnitude relations are established between Mw,Global CMT and Ms, mb, and ML reported by the ISC, NEIC, IDC, and NDI, and compared with the previously developed regional and global regression relations. The duration (MD) and local (ML) magnitudes reported by NDI exhibit a 1:1 relationship. The derived magnitude regression relations are expected to support the homogenization of the earthquake catalogs and to improve seismic hazard assessment in this region.

Impact of earthquakes and its dependence on magnitude: testing the Greek seismicity

<p>Strong earthquakes cause significant impact on both the built and natural environment. Impact databases are of fundamental importance for seismic risk assessment in a region. Such data include human and property losses as well as secondary effects including ground failures and tsunamis. The earthquake impact, EI, depends on many factors, one of the most important being the earthquake magnitude, M. To test the dependence of EI on M we selected the Greek seismicity which is the highest in the Mediterranean region with record of earthquakes since the antiquity. Although various descriptive and parametric earthquake catalogues as well as inventories of intensity observation points are available for Greece no database for EI has been organized so far. For a first time we organized a Greek Earthquake Impact Database (GEID) which covers the time interval from 1800 to 2019 and includes earthquake parameters and three main quantitative impact elements: building damage, fatalities and injuries. Data on tsunami impact are also included in the GEID. A long number of sources have been utilized, some of them remaining unknown so far in the seismological community. To select the most appropriate magnitude for each earthquake event occurring in the instrumental period of seismology, i.e. from 1900 onwards, we compared the catalogues produced by the ISC-GEM and by three academic institutions. After completeness testing and examination for magnitude homogeneity we performed magnitude closeness analysis and produced formulas for magnitude conversion from one catalogue to another. For the 19<sup>th</sup> century earthquakes we again compared various catalogues, collected new data from documentary sources and compiled a new catalogue by re-calculating macroseismic magnitudes equivalent to Mw from intensity/M relations developed for Greek earthquakes of the instrumental period. We found that for single earthquake events the level of impact generally depends on magnitude but this is not valid for offshore events. However, the time distribution of the three impact elements over the period examined showed a relative decrease of the totally collapsed buildings which implied drastic decrease of the fatality rate but not of the injuries rate. This is attributed to the gradual improvement of the building construction particularly after the enforcement of antiseismic building codes in the country. Τhe first author was supported by the Hellenic Foundation for Research and Innovation (HFRI) and the General Secretariat for Research and Technology (GSRT), under the HFRI PhD Fellowship grant (GA. no. 490).</p>

An updated and unified earthquake catalog from 1787 to 2018 for seismic hazard assessment studies in Mexico

Here we present a new updated and unified Poissonian earthquake catalog for Mexico. The details about the catalog compilation, the removal of duplicate events, unifying the magnitude scales, removal of dependent events through the declustering process and its completeness analysis are presented. Earthquake and focal mechanism data have been compiled from various local, regional and international sources. Large earthquake events (MW ≥ 6.5) have been carefully revised for their epicentral locations and magnitudes from trusted publications. Different magnitude-conversion relationships, compatible with available local and regional ones, has been established to obtain unified moment magnitude estimates for the whole catalog. Completeness periods for the declustered catalog were estimated for the definition of appropriate seismic source models for the whole territory. The final unified Poissonian earthquake catalog spans from 1787 to 2018, covering a spatial extent of 13° to 33°N and 91° to 117°W. This catalog is compatible with other published catalogs providing basis for new analysis related to seismicity, seismotectonics and seismic hazard assessment in Mexico.