The Erzincan (Turkey) Earthquake (Ms 6.8) of March 13, 1992 and its Aftershock Sequence

—The Erzincan strike-slip earthquake of March 13, 1992 ruptured a section of the North Anatolian fault (NAF) at the northern margin of the Erzincan basin. The focal depth of about 10 km was less than given by ISC and NEIC. Erzincan and the surrounding villages were considerably damaged. In the Erzincan basin and in the neighbouring mountains a seismic network of ten stations was installed. It was operating continuously from March 21 through June 16, 1992. More than 3,000 aftershocks were recorded of which 505 could be located. The spectral parameters of 394 and the fault-plane solutions of 53 aftershocks were determined. For the given region the frequency dependent coda Q was derived as Q _c = 122 f ^0.68. The aftershock area increased with time, reflecting the process of stress redistribution. Some events clustered in the immediate vicinity of the town of Erzincan close to the epicentre of the main event and seem to trace the NAF. Their source mechanism is similar to that of the main event (strike slip). About 150 aftershocks clustered in the southeastern part of the Erzincan basin where a concentration of the events in a small volume of 5 × 5 × 3 km³ was observed. The majority of fault-plane solutions available for these aftershocks showed a normal faulting mechanism with an east-west directed extension. Most of the aftershocks southeast of the basin clustered between two lineaments that were mapped by satellite images. The P-wave velocity below the Erzincan basin, derived from travel-time residual analysis, is lower compared to areas NE and SW of the basin. Three-dimen sional stress modelling of the Erzincan region qualitatively explains the occurrence of the aftershocks southeast of the basin. The calculated displacement distribution which exhibits the north-westward motion of the basin and tension at its southeastern margin, caused by the Erzincan earthquake, is in agreement with derived fault-plane solutions.     

The Characteristic Analysis and Seismic Triggering Study of the M6.2 and M6.1 Dayao Earthquake Sequences in 2003

INTRODUCTIONTheM6·2 andM6·1 earthquakes occurred successivelyin Dayao,Yunnan Province on July 21and October 16 ,2003 and bothinduced human casualty and economic loss to some extent .Adequatehistorical information reveals that ,earthquakes bigger thanM6·0 in Yunnan are distributed mainlyalong some active tectonic faults and seismic belts . Dayao and Yao an are in the Dianzhong tectonicblock andthere are noapparentfaultsthere(Su Youjing,2004) .Seismic activitylevel inthisregioniswea…     

Aftershock Statistics of the 1999 Chi–Chi, Taiwan Earthquake and the Concept of Omori Times

In this paper we consider the statistics of the aftershock sequence of the m = 7.65 20 September 1999 Chi–Chi, Taiwan earthquake. We first consider the frequency-magnitude statistics. We find good agreement with Gutenberg–Richter scaling but find that the aftershock level is anomalously high. This level is quantified using the difference in magnitude between the main shock and the largest inferred aftershock $ {{\Updelta}}m^{ *}. $ Typically, $ {{\Updelta}}m^{ *} $ is in the range 0.8–1.5, but for the Chi–Chi earthquake the value is $ {{\Updelta}}m^{ *} $  = 0.03. We suggest that this may be due to an aseismic slow-earthquake component of rupture. We next consider the decay rate of aftershock activity following the earthquake. The rates are well approximated by the modified Omori’s law. We show that the distribution of interoccurrence times between aftershocks follow a nonhomogeneous Poisson process. We introduce the concept of Omori times to study the merging of the aftershock activity with the background seismicity. The Omori time is defined to be the mean interoccurrence time over a fixed number of aftershocks.     

Seismogenic Structure of the 1411 Southern Damxung (Damdoi) Earthquake with M=8 in Tibet

The seismogenic structure of the 1411 southern Damxung(Damdoi)earthquake with M=8 in Tibet is discussed in detail in this paper.It is pointed out that the Nyainqentanglha southern pediment fault is the seismogenic one of the 1411 southern Damxung(Damdoi)earthquake with M=8,and the macroepicenter is located at the intersection of the extensional shear fault within Nasego-Garbogo pull-apart basin and the secondary strike-slipping fault with larger amplitude of neotectonic activity at the southwestern side of the basin.Besides,there is obvious anomaly of the geophysical fields in the seismic area,indicating that occurrence of 1411 southern Damxung(Damdoi)earthquake with M=8 was not only controlled by the superstructure but also the background of deep-seated structure.     

Investigation on the Site of the 2003 South Bomi (Tibet) M_S5.7 Earthquake

INTRODUCTIONAs registered by the seismic network of the China Earthquake Administration and the regionalnetworkof Xizang(Tibet) Autonomous Region,anMS5·7 earthquaketook place between Bomi countyand Medog county, Tibet on August 18 , 2003·The China Earthquake Administration sent anearthquake site investigation team to the stricken region immediately after the earthquake . Theinvestigationteamconsistedjointly of personnel fromthe Earthquake Administration of Xizang (Tibet)Autonomo…     

Assessment of the Seismic Situation in the Region of Greece’s Eastern Coast of the Aegean Sea before the Earthquake with M = 6.7 (October 30, 2020)

Izvestiya, Physics of the Solid Earth - Abstract—A detailed study has been carried out regarding temporal variations of seismicity in the region of Greece’s eastern coast of the Aegean...     

Double-difference Relocation of the Aftershocks of the Tecom��n, Colima, Mexico Earthquake of 22 January 2003

On 22 January 2003, the M _w?=?7.6 Tecomán earthquake struck offshore of the state of Colima, Mexico, near the diffuse triple junction between the Cocos, Rivera, and North American plates. Three-hundred and fifty aftershocks of the Tecomán earthquake with magnitudes between 2.6 and 5.8, each recorded by at least 7 stations, are relocated using the double difference method. Initial locations are determined using P and S readings from the Red Sismológica Telemétrica del Estado de Colima (RESCO) and a 1-D velocity model. Because only eight RESCO stations were operating immediately following the Tecomán earthquake, uncertainties in the initial locations and depths are fairly large, with average uncertainties of 8.0?km in depth and 1.4?km in the north?Csouth and east?Cwest directions. Events occurring between 24 January and 31 January were located using not only RESCO phase readings but also additional P and S readings from 11 temporary stations. Average uncertainties decrease to 0.8?km in depth, 0.3?km in the east?Cwest direction, and 0.7?km in the north?Csouth direction for events occurring while the temporary stations were deployed. While some preliminary studies of the early aftershocks suggested that they were dominated by shallow events above the plate interface, our results place the majority of aftershocks along the plate interface, for a slab dipping between approximately 20° and 30°. This is consistent with the slab positions inferred from geodetic studies. We do see some upper plate aftershocks that may correspond to forearc fault zones, and faults inland in the upper plate, particularly among events occurring more than 3?months after the mainshock.     

The Dinar Earthquake (Mw = 6.2; October 1, 1995; Afyon-Turkey) and Earthquake Hazard of the Dinar-Çivril Fault

—A moderately strong earthquake (M _w = 6.2) occurred in the town of Dinar at 17.57 UT on October 1, 1995, taking the lives of 90 people and damaging about 4500 buildings. Its epicenter is located near the Dinar-Çivril fault and its focal mechanism is linked to a northeast-southwesterly tensional stress field arising from the interaction between the subducting African plate and the overriding Aegean-Anatolian plate in the eastern Mediterranean.¶Surface cracks of the October 1 earthquake have been observed 10 km continuously along the Dinar-Çivril fault. The cracks have displayed a mode of dip-slip; however, some have also indicated lateral slip. The different modes of slip are generally in agreement with the fault plane solution and are indicators of the complex nature of the rupture process.¶In investigating the earthquake hazard of the Dinar-Çivril fault and proximity, the maximum likelihood method was used to estimate seismic hazard parameters of b-value, seismicity activity rate λ _m and the expected maximum magnitude M _max?. The data consisted of the historical data covering the period between 1800–1900 and instrumental data between 1900 and 1992. This method, allowing use of the mixed earthquake catalogue containing both historical and instrumental earthquake data, yielded values of 0.70, 1.92 and 7.14 for b, λ _m and M _max?, respectively. The recurrence time estimated for an earthquake of a magnitude of M _w = 6.2 is 123 years. The non-occurrence probabilities of such an earthquake in 1 and 50 years are 0.21 and 0.04, respectively.     

Evolution of 3D velocity structure before Dayao M=6.2 and M=6.1 earthquakes in 2003

Introduction The Sichuan-Yunnan rhombic block (KAN et al, 1977) located to the southeast of Qinghai-Xizang (Tibetan) sub-plate is one of the most seismically active tectonic regions and ac- tive region of strong earthquakes to monitor (MA et al, 1987). Af…     

Source Characteristics of the 22 January 2003 M w?=?7.5 Tecom��n, Mexico, Earthquake: New Insights

Aftershock locations, source parameters and slip distribution in the coupling zone between the overriding North American and subducted Rivera and Cocos plates were calculated for the 22 January 2003 Tecomán earthquake. Aftershock locations lie north of the El Gordo Graben with a northwest-southeast trend along the coast and superimposed on the rupture areas of the 1932 (M _w?=?8.2) and 1995 (M _w?=?8.0) earthquakes. The Tecomán earthquake ruptured the northwest sector of the Colima gap, however, half of the gap remains unbroken. The aftershock area has a rectangular shape of 42?±?2 by 56?±?2?km with a shallow dip of roughly 12° of the Wadati-Benioff zone. Fault geometry calculated with the Náb??lek (1984) inversion procedure is: (strike, dip, rake)?=?(277°, 27°, 78°). From the teleseimic body wave spectra and assuming a circular fault model, we estimated source duration of 20?±?2?s, a stress drop of 5.4?±?2.5?MPa and a seismic moment of 2.7?±?.7?×?10²⁰?Nm. The spatial slip distribution on the fault plane was estimated using new additional near field strong motion data (54?km from the epicenter). We confirm their main conclusions, however we found four zones of seismic moment release clearly separated. One of them, not well defined before, is located toward the coast down dip. This observation is the result of adding new data in the inversion. We calculated a maximum slip of 3.2?m, a source duration of 30?s and a seismic moment of 1.88?×?10²⁰?Nm.     

Relocation of the October 9, 1505 Earthquake with M63/4

There have been 12 possible locations of the earthquakes occurring in the South Yellow Sea since 1505.In this paper,the location of the earthquake that occurred in 1505 has been determined by the collection of more historical data of the influenced field,referring the isoseismal data of earthquakes with the epicentral intensityⅨ and combining geophysical field data with tectonic condition,due to its great influence on seismic safety assessment of some significant engineering.     

Process of source dynamics of the Jingtai earthquake (M=6. 2 )

ＰｒｏｃｅｓｓｏｆｓｏｕｒｃｅｄｙｎａｍｉｃｓｏｆｔｈｅＪｉｎｇｔａｉｅａｒｔｈｑｕａｋｅ（Ｍ＝６．２）Ｘｕｅ－ＢｉｎＤＵ（杜学彬）；Ｚｈｉ－ＤｅＹＡＮ（闫志德）ａｎｄＭｉｎｇ－ＷｕＺＯＵ（邹明武）（ＥａｒｔｈｑｕａｋｅＲｅｓｅａｒｃｈＩｎｓｔｉｔｕ...     

Earthquake probabilities and magnitude distribution (M ≥ 6.7) along the Haiyuan fault, northwestern China

Introduction Haiyuan fault is a major seismogenic fault in north-central China. One of the most devastat-ing great earthquake in the 20th century occurred near Haiyuan in northwestern China on Decem-ber 16, 1920. More than 220 000 people were killed and thousands of towns and villages weredestroyed during the devastating earthquake. A 230 km long left-lateral surface rupture zone wasformed along the Haiyuan fault during the earthquake with maximum left-lateral displacement of10 m. Pale…     

Crustal Movements and Deformations in Eastern Turkey in Connection with the Van Earthquake (October 23, 2011, Мw = 7.2): Study from GPS Data

Izvestiya, Physics of the Solid Earth - Abstract—A devastating earthquake with magnitude Mw = 7.2 occurred in the Van region, Eastern Turkey, on October 23, 2011. This study analyzes the...     

Using an Enhanced Dataset for Reassessing the Source Region of the 2003 Armer��a, Mexico Earthquake

We present a fresh look at the source region of the 22 January 2003 M _w 7.4 Armería earthquake, which occurred off the Pacific coast of the state of Colima, Mexico, near the town of Armería. The effects of this earthquake in the neighboring states of Colima and Jalisco were different and stronger than those of previous recent major earthquakes in the region. This earthquake and its aftershocks were recorded by two local telemetered seismograph networks (RESCO and RESJAL). From 22 January to 24 January 2003, no important seismicity was located on the plates interface, or within the Rivera Plate, and most epicenters were located west of the Armería River, which is the western border of the Colima Graben, and is located outside of the Colima Gap region. From 24 January to 31 January, the seismicity recorded by both networks showed a migration in depth, with an almost vertical offshore distribution between 4 and 24?km in depth. For this period, a seven-station portable digital seismograph network, equipped with three-component seismometers, was deployed in the epicentral area to study the aftershock sequence in detail. With this denser network more than 200 M _L?>?2.0 aftershocks were recorded. The aftershock foci were deeper than those recorded during the early period and most of them locate on a hypothetical 12° dipping interface between the Rivera and North American Plates. Composite focal mechanism solutions for the aftershocks located during both periods indicate a reverse fault character that changes with time. Analysis of the new dataset still indicates that the earthquake was a shallow intraplate event.     

Source parameters for the M<Subscript>w</Subscript> = 6.6, 03 February 2002, Çay Earthquake (Turkey) and aftershocks from GPS,Southwestern Turkey

The 03 February 2002 Çay Earthquake (M_w ～6.7) occurred on the fault segment between Eber and Ak?ehir Lakes followed by a large aftershock (M_w ～5.6) near the western end of the fault and two sequential aftershocks. We computed the coseismic surface displacements from static GPS measurements to determine the fault geometry parameters and uniform slip components. The coseismic displacements were obtained through combining the regional pre-earthquake and post-earthquake GPS data. Fault geometry and slips were acquired through the inversion of GPS data modeling the events as elastic dislocations in a half-space and assuming all four events took place on the same fault plane. Results suggest that one-segment fault of ～33 km length and dipping ～43° northward suffices to model the dislocation, assuming uniform slip distribution with 0.51 m dip slip, 0.26 m left-lateral slip extending to a depth down to ～11.5 km which is consistent with seismological evidence. The results also verify the normal faulting in the eastern flank of Isparta Angle which has long been assumed as a thrusting structure. While the available data cannot identify the four individual events on the same day, an attempted distributed slip model differentiates dip slip and left-lateral slips near the hypocenter with maximum values of ～1 and 0.6 m, respectively.     

Studies on the Surface Rupture Zone of 1303 Hongdong Earthquake of M =8 and Paleoearthquakes of Huoshan Fault in Shanxi Province

An earthquake of M=8 occurred in the Linfen Basin of the Shanxi graben system in 1303,producing a surface rupture zone about 45km long.Compiling a geological map at 1:10,000 and studying in detail the rupture zone,its dextral strike-slip displacement is determined to be 4-8.6 m,and normal dip-slip displacement up to 3.5-5 m.In this paper the geochronological evidence for the formation of the surface rupture zone is provided and the Huoshan fault is confirmed to be the seismogenic structure for the M=8 earthquake.Field trenching enables us to identify two paleoseismic events having occurred along the Huoshan fault since the middle Holocene before the M8 earthquake.A recurrence interval of these three events including 1303 Hongdong M 8 earthquake is determined to be up to 1500-2000 years.The result corresponds to the mean recurrence interval calculated from slip rate on the Huoshan fault during Holocene.     

Investigation of rupture process of the 1999 M=5.4 Xiuyan, Liaoning, earthquake sequence

As is well known, researches on rupture process of earthquakes can not only deepen our understanding of earthquake occurrence, but also help to achieve earthquake prediction, which is one of the most difficult scientific problems in the world. Seismologists always pay great attention to it. Since the beginning of 1990s, they have aimed at the time-space variation of earthquake source rupture during the mainshock. In their works the digital data of seismic waves are inverted for the rupture pro…     

Şarköy-Mürefte 1912 Earthquake's Tsunami, extension of the associated faulting in the Marmara Sea, Turkey

The historical tsunamis in the Marmara Seawere mainly caused by earthquakes andneeded to be documented. Following 1999Izmit earthquake occurred at the EasternMarmara region, a complete inventory ofactive faults in the Marmara Sea regionbecame much more stressed. To the west, thelatest event is 09.08.1912arköy-Mürefte Earthquake. Itoccurred on the active Ganos Fault zone andwas one of the largest earthquakes in theBalkans. The eastern termination of theassociated faulting is in the deep WestMarmara Trough, westernmost of thesuccessive basins forming the Marmara Sea.On the basis of recent multibeam bathymetryand seismic reflection data, estimatedtotal length of the surface rupture isabout 56 km. The historical data reviewedfrom library and archive documents,geological field surveys and offshoregeophysical investigations have shown thatthe 1912 earthquake produced a tsunami. Inaddition a seabed dislocation, the sourceof 1912 tsunami can also be assigned to thesediment slumps appearing in the form ofechelon landslide prisms along the southernslopes of the West Marmara Trough.