Modified Joint Hypocenter Determination Research Articles

COMPARISON OF EARTHQUAKE HYPOCENTER RELOCATION METHODS IN THE JAVA REGION, INDONESIA

Java is a frequent island of earthquakes caused by the subduction of the Indo-Australian plate under the Eurasian plate. The mitigation of earthquake disasters is by relocating the hypocenter. Hypocenter relocation was conducted in order to obtain a more accurate earthquake position, which can be used to interpret the structure under the earth's surface. The Modified Joint Hypocenter Determination (MJHD) and Double Difference (DD) methods are required when applying earthquake hypocenter relocation. The objective of research is comparing the relocation results in the Java region with the Modified Joint Hypocenter Determination (MJHD) and Double Difference (DD) Methods for obtaining the distribution of earthquake hypocenters before and after relocation. The study has obtained arrival time data in the form of BMKG catalog data from the period of January 1, 2022 through May 30, 2022 in the Java area with the coordinates of 6.0 LS - 12.0 LS and 106.0 BT - 114.0 BT. The MJHD method compares the travel time difference of a set of data that occurs simultaneously in order to obtain a more accurate hypocenter position, while the DD method compares the hypocenter distance of the two earthquakes with the station distance, so that Ray Path and Waveform are considered equal. The relocation of the initial earthquake has a depth of 10 km, resulting in a shift of shallow earthquakes clustered in the active fault section, while deep earthquakes are clustered in the subduction zone section. The results of relocation with the MJHD method obtained 637 earthquakes.

Determination of Earthquake Hypocenter Distribution using the Modified Joint Hypocenter Determination (MJHD) Method throughout the Palu-Koro Fault (Case Study: August-October, 2018)

The area of Sulawesi, especially along the Palu Koro Fault, is an area that is largely influenced by the confluence and movement of plates as well as regional fault activity pathways with high levels of seismicity. Determining the location of the hypocenter accurately through relocation is required in identifying the detailed tectonic structures in the area. Relocation of the hypocenter using the Modified Joint Hypocenter Determination (MJHD) method using the IASP91 velocity model in the period August to October 2018 with the arrival time data from BMKG catalog. The results of hypocenter relocation using the MJHD method show that from 132 earthquake distribution points to 63 earthquake hypocenter points after the relocation. The change in the location of the hypocenter was much denser along the Palu Koro Fault route than before the relocation as evidenced by the mean value of rms (root mean square) before relocation was 1.31 and after relocation it became smaller (0.61). Changes in parameter values after relocation using the MJHD method caused the distribution of the earthquake hypocenter to be tighter towards the Palu Koro fault than before the relocation, where the distribution had a random and scattered pattern.

Hypocenter relocation and velocity model for major earthquakes in northwest Himalaya

The proper understanding of earthquake geometry and location is very important to understand the seismicity of an area. In the present study, 185 earthquakes that occurred in the northwest Himalaya of magnitude Mw > 0.6 between 2010 and 2013 were relocated using the Modified Joint Hypocenter Determination method. After examining seven velocity models, average VP/VS ~ 1.73 computed by Wadati diagram is used to improve the hypocenter locations of the earthquakes. Based on hypocentral distributions, these earthquakes were classified into four groups. Group 1 is along the Punjal Thrust in Hazara Kashmir Syntaxes. Group 2 belongs to the Indus-Kohistan Seismic Zone whereas group 3 is along the Besham dome and the fourth group is along the Main Mantle Thrust. Shallow crustal earthquakes were relocated to 0–50 km, deep earthquakes were relocated to 50–100 km, and much deep earthquakes were relocated to 250–350 km depth. This analysis will be helpful to understand the seismicity of the northwest Himalaya of Pakistan.

KOREKSI LOKASI HIPOSENTRUM GEMPABUMI DI SULAWESI UTARA MENGGUNAKAN METODE MODIFIED JOINT HYPOCENTER DETERMINATION

North Sulawesi is one of the areas that has had a fairly high level of seismic activity that has occurred, due to the position of North Sulawesi Island which is located close to the earthquake source. One of the parameters of an earthquake that can be calculated is the earthquake hypocenter.Determining the hypocenter of an earthquake is very important in the world of seismology. The Modified Joint Hypocenter Determination (MJHD) method was carried out for relocation of the earthquake hypocenter. To find out how the results of the Hypocentrum Location Correction using MJHD and the tectonic pattern of the Sulawesi Sea Plate subduction zone. . The results of relocation using the MJHD (Moodifide Joint Hysopcentrum) method showed better and more accurate data quality seen from the residual value (RMS) before (≥1 s) and after relocation (≤1 S). Based on the seimicity results of relocation using the MJHD method, it was found that the earthquake clusters were concentrated at a shallow depth of the range of 20 - 80 km. At a depth of 250 - 300 and a distance of 400 km, there is a seimic gap so that earthquakes rarely occur in this zone.

Analysis of the mentawai region fault field based on earthquake relocation data using the modified joint hypocenter determination (MJHD) method

Tectonic conditions in an area are very important to know, one of them is the Mentawai region. Mentawai is an area prone to earthquake disasters, this is because the Mentawai is located between the subduction zone between the Eurasian Plate and the Indo-Australian Plate. One of the earthquake parameters that is needed in analyzing tectonic conditions is the hypocenter. Accurate hypocenter determination can be done by relocating earthquakes using the Modified Joint Hypocenter Determination (MJHD) method. The MJHD method is carried out by inversion of the main earthquake and aftershocks with correction of the station at the earthquake event. The earthquake data in this study began on September 1, 2017, until December 31, 2018, with 1 main earthquake and 104 aftershocks in the format of arrival time. The main earthquake before the relocation is at longitude coordinates 99.85o latitude -2.6o with a depth of 12 km. After being relocated it is at coordinates 99.5413o latitude 2.5779o with a depth of 29 km. The results after the relocation were identified were fault fields occurring in the B-B cross-section ‘nodal plane 2 with a strike of 141o 66o slip 92o. Earthquake relocation using the Modified Joint Hypocenter Determination (MJHD) shows a change in the Root Mean Square (RMS) value <1. This suggests that the earthquake hypocenter after relocation using the Modified Joint Hypocenter Determination (MJHD) method is more accurate.

RELOKASI HIPOSENTER GEMPABUMI MENGGUNAKAN METODE MODIFIED JOINT HYPOCENTER DETERMINATION (MJHD) UNTUK ANALISIS ZONA SUBDUKSI SUMATERA BAGIAN SELATAN

The part of south Sumatera is very vulnerable region in case of earthquake disaster caused by convergent boundary of two tectonic plates Indo-Australian Plates and Eurasian Plates. Precise hypocenter analysis is needed to understand about the accurate tectonic setting such as subduction zone in the area. Hypocenter relocation is used to recalculate earthquake hypocenter to become more accurate. To produce a more accurate hyposenter this hyposenter relocation is done by using the method of Modified Joint Hypocenter Determination (MJHD). Relocation using the Modified Joint Hypocenter Determination (MJHD) method uses IASP91 wave velocity which assumes that the inner structures are heterogeneous. In this study, used data P-wave and S-wave arrival time in the period January 2010 s.d December 2016 with coordinates -3.5º s.d -9º LS - 99º s.d 106.5º BT. The results of the relocation using MJHD showed a change of earthquake hypocenter shown by RMS (Root Mean Square) value ranging from 0.2 s.d 0.5. There are three subduction of the part in south sumatra. The subduction zone formed in Bengkulu is about 26.78º, the subduction zone of Lampung is around 30.225º and the subduction of the Sunda Strait is about 52.53º. Subduction zone of Bengkulu at depth of 250 km, Lampung and Sunda Strait at depth 400 km.

Microearthquake relocation hypocenter using Modified Joint Hypocenter Determination (MJHD) method. (case study: Opak fault)

Earthquakes with small magnitude and shallow depths are one form of manifestation of existence a fault line in Yogyakarta. Accurate hypocenter determination is needed to identify tectonic and fault conditions based on earthquake hypocenter distribution recorded by seismograf. Hypocenter was determined by using two methods Geiger’s Adaptive Damping for early hypocenter and Modified Joint Hypocenter Determination (MJHD) for relocate hypocenter, we used 2 weeks aftershock data after main quake occurred on June 10-14 2006 with total of 625 events earthquake obtained from the results of picking waves. The difference of hyposenter result on the longitude and latitude is about 2 -25 km and depth change around 0.3-5 km with major distribution to the east from the fault. The final result of this relocation shows that the area is more easily releases energy is in the eastern section of the fault consisting of sedimentary rocks.

Earthquake History of the Sumatran Fault, Indonesia, since 1892, Derived from Relocation of Large Earthquakes

Abstract We map the fault planes of M ≥7.0 earthquakes along the Sumatran fault in Sumatra, western Indonesia, for the period since 1892. To obtain precise hypocenter locations of large earthquakes and identify fault planes of M ≥7.0 earthquakes, we relocated 27 M ≥6.0 earthquakes from 1921 to 2012 using the modified joint hypocenter determination method. We found that six M ≥7.0 events appear to have occurred on segments of the Sumatran fault as follows: Kumering for the 1933 ( M s 7.5) event; the northwestern and southeastern parts of Tripa for the 1935 ( M s 7.0) and 1936 ( M s 7.2) events, respectively; the southeastern half of Sunda for the April 1943 ( M s 7.1) event; Ketaun for the first ( M s 7.3) event of the June 1943 doublet; and Suliti and Sumani for the second ( M s 7.6) event of the June 1943 doublet. We also identified the faults of four M ≥7.0 earthquakes between 1892 and 1920 by using information on crustal deformation and damage distributions. From the results of earthquake locations between 1892 and 2012, and the corresponding fault lengths of M ≥7.0 earthquakes, we have interpreted the large ( M ≥7.0) earthquake history of the Sumatran fault for the past 120 years. Possible seismic gaps for M ≥7.0 earthquakes along the Sumatran fault are the northern half of the Sunda segment, and the Semangko, Dikit, Sianok, Barumun, Toru, Renun, Aceh, and Seulimeum segments.

Fault plane of the 1964 Niigata earthquake, Japan, derived from relocation of the mainshock and aftershocks by using the modified joint hypocenter determination and grid search methods

We relocated the mainshock and immediate aftershocks of the 1964 Niigata earthquake (Ms 7.5) using both the modified joint hypocenter determination (MJHD), and the grid search (GS), methods to obtain their hypocenters and identify the fault plane of the mainshock. We used P-wave arrival times at 13 Japanese stations reported by the Japan Meteorological Agency (JMA). Firstly, we performed the MJHD method to select readings with high accuracies and to obtain station corrections that related to the lateral heterogeneity of the Earth’s structure. Secondly, we performed the GS method by using only selected readings and assuming the station corrections. Based on the relocated hypocenters, we found that the mainshock and immediate aftershocks occurred along a plane striking N15°E and dipping 11° eastward. This result strongly suggests that one of the nodal planes of the mainshock, for which the strike and dip are N9°E and 34°, respectively, is preferable as the fault plane. When global stations are also used for relocations, the results confirm that the fault plane of the 1964 Niigata earthquake dips gently eastward. Therefore, we concluded that the fault plane of the 1964 Niigata earthquake is gently eastward-dipping.

Relocation of the 2011 off the Pacific coast of Tohoku earthquake sequence and fault planes of M ≥ 7 earthquakes

We relocated foreshocks, mainshock, and aftershocks of the 2011 off the Pacific coast of Tohoku Earthquake (Mw 9.1) using the modified joint hypocenter determination (MJHD) method in order to obtain their precise hypocenters and to identify fault planes of larger earthquakes. We used P-wave arrival times at stations worldwide reported by the U.S. Geological Survey (USGS). We confirmed by relocated hypocenters that the mainshock and aftershocks had occurred along the plate boundary between the North American and Pacific plates. We also confirmed that the Mw 7.5 foreshock, which occurred two days before the mainshock, and the largest aftershock (Mw 7.9), which occurred half an hour after the mainshock, were thrust earthquakes along the plate boundary. The second largest aftershock (Mw 7.6), which was a normal-faulting earthquake and was a bending-stress intra-plate event caused by the strain reduction on the subduction thrust, occurred at the outer rise of the Japan Trench and was well relocated with its aftershocks. We found that its fault plane dipped westward and it bounded the aftershock distribution on the seaward side. This implies that the western side of the fault plane had subsided, corresponding with the westward plate subduction.

Two seismic gaps on the Sagaing Fault, Myanmar, derived from relocation of historical earthquakes since 1918

[1] Relocation of six M (magnitude) ≥ 7.0 earthquakes near the Sagaing Fault in Myanmar since 1918 allows us to image earthquake history along the Sagaing Fault. All the earthquakes were relocated on the Sagaing Fault by using the modified joint hypocenter determination method. Combining the relocated epicenters with information on foreshocks, aftershocks, seismic intensities, and coseismic displacement, we estimated the location of the fault plane that ruptured during each earthquake. This analysis revealed two seismic gaps: one between 19.2°N and 21.5°N in central Myanmar, and another south of 16.6°N in the Andaman Sea. Considering the length of the first seismic gap (∼260 km), a future earthquake of up to M ∼7.9 is expected to occur in central Myanmar. Because Nay Pyi Taw, the recently established capital of Myanmar, is located on the expected fault, its large population is exposed to a significant earthquake hazard.

Interpretation of the 1993, 2001, and 2002 Guam Earthquakes as Intraslab Events by a Simultaneous Relocation of the Mainshocks, Aftershocks, and Background Earthquakes

It has been unclear whether the 1993, 2001, and 2002 Guam earthquakes ( M w 7.8, 7.0, and 7.1, respectively) in the southern Mariana subduction zone were interplate events or intraplate ones within the Pacific slab. We relocated their mainshocks, aftershocks, and numerous long-term background earthquakes simultaneously with high relative accuracy using the modified joint hypocenter determination (MJHD) method. As a result, their mainshocks and three-day aftershocks are clearly distributed within the background slab seismicity. Therefore, we conclude that the 1993, 2001, and 2002 Guam earthquakes were not interplate events, which scarcely occur in the Mariana subduction zone, but intraslab earthquakes within the subducted Pacific plate. The 1993 fault plane is inferred to be the near-horizontal nodal plane of the mechanism solution, though the 2001 and 2002 fault planes remain unknown. The relocation of target events simultaneously with background earthquakes has turned out very effective for discriminating between large interplate and intraslab earthquakes in subduction zones.

Relocation of large intermediate-depth earthquakes in the Vrancea region, Romania, since 1934 and a seismic gap

AbstractWe relocatedM6 or larger intermediate-depth earthquakes in Vrancea, Romania that have occurred since 1934. To determine their absolute hypocenters accurately, we combined them with recent (from January 1996 to November 2003) smaller earthquakes recorded by the Romanian local network and then relocated all of them simultaneously using a modified joint hypocenter determination method. Using the data on recent small earthquakes we first obtained an estimate of the dimensions of the active seismic region of intermediate-depth earthquakes: length, 85 km; along a NE-SW direction; width, 20 km; depth 60-160 km. We then determined that the 1940 (M7.7), 1977 (M7.5) and 1990 (M6.9) major earthquakes were located near the NE edge of the seismic region, while the 1986 (M7.2) was located inside the seismic region. The focal depths of the 1940, 1977, 1986 and 1990 major earthquakes were calculated to be 124, 98, 135 and 84 km, respectively and their source areas to range from 60 to 140 km in depth. The only unbroken area is at a depth of 140–160 km, which we current consider to be a seismic gap. Based on the regularity of past large earthquakes, we propose that the nextM7 intermediate-depth earthquake can be expected to occur in Vrancea at a depth interval of 140–160 km sometime early in this century.

Two parallel trench-normal fault planes within the Pacific slab associated with the 1994 and 2000 Kurile earthquakes as revealed by simultaneous relocation of their main shocks and aftershocks

Abstract The 1994 Hokkaido-Toho-Oki (M w 8.3) and the 2000 Nemuro-Hanto-Oki (M w 6.8) earthquakes have been regarded as great/large intraslab events within the subducted Pacific plate along the southern Kurile trench. Determining which nodal planes of their mechanism solutions are actual fault planes and whether or not the 2000 event occurred on the southwestern extension of the 1994 fault plane have been problematic. In order to clarify these points, we examine the relative location of their main-shock and aftershock distributions accurately by simultaneous relocation of their hypocenters using the Modified Joint Hypocenter Determination (MJHD) method. The result clearly shows that the two earthquakes occurred on trench-normal shallow-dipping fault planes within the Pacific slab, apart from and parallel to each other. Therefore, the 2000 earthquake was not a rupture on the deeper extension of the 1994 fault plane, but one on another fault plane. A large intraslab earthquake (M w 7.8; depth, about 100 km) occurred to the northwest of the 1994 event in 1978, and two trench-normal fracture zones exist outside the trench to the southeast of the 1994 and 2000 events. Therefore, these three intraslab great/large earthquakes are considered to have been ruptures along pre-existing trench-normal weak zones within the subducted Pacific plate.

The 1998 Papua New Guinea Earthquake and its Fault Plane Estimated from Relocated Aftershocks

The 1998 Papua New Guinea earthquake of M w 7.0 occurred near the Wewak trench where the North Bismarck plate is subducting beneath the Australian plate. Its mechanism is thrust-type, and one of the nodal planes is almost parallel to the plate interface. To determine which of the two nodal planes of the main shock is the fault plane, we relocated the main shock and aftershocks using a method of modified joint hypocenter determination. We combined and employed two types of data in this study. Firstly, we used data reported by the National Earthquake Information Center (NEIC) of the U.S. Geological Survey (USGS), which includes three stations at the northeastern edge of Irian Jaya and one station in northern Papua New Guinea, from which the epicentral distances are less than 2 degrees. Secondly, in addition to the above permanent-station data, we used data from temporary aftershock observations near the epicentral area around the Sissano Lagoon carried out by TsuJI et al. (1998). Using three-component seismometers, they carried out observations from August 2 to October 2, 1998 at three sites. Although the network did not record the main shock and immediate aftershocks, the data obtained by temporary observation sites can clearly assist in identifying their absolute locations, since it is possible to apply the joint hypocenter determination (JHD) method. Hypocenters were relocated between the coastline and the Wewak trench, distributed along a nodal plane dipping shallowly to the southwest. Therefore, we can conclude that this nodal plane is the main shock fault and that the 1998 Papua New Guinea earthquake was an interplate earthquake between the North Bismarck and Australian plates.

The 1995 off-Etorofu earthquake: Joint relocation of foreshocks, the mainshock, and aftershocks and implications for the earthquake nucleation process

Abstract Prominent foreshock activity preceded the Mw 7.9 off-Etorofu earthquake in the Kurile Islands on 3 December 1995. Using a modified joint hypocenter determination method (Hurukawa, 1995), we simultaneously relocated foreshocks, the mainshock, and aftershocks to study the foreshock activity in detail in view of the nucleation process of a large earthquake. The distribution of relocated earthquakes and their focal mechanisms suggest that the 1995 off-Etorofu earthquake was an interplate earthquake at the boundary between the North American and Pacific plates. Its source area overlaps with those of the 1958 off-Etorofu (Mw 8.3) and the 1963 off-Urup (Mw 8.5) earthquakes. Nine days before the occurrence of the mainshock, a first immediate foreshock of magnitude 6.4 occurred at the deepest point of the foreshock area. This event was followed by many foreshocks, including three additional M ≧ 6 events, which occurred east and southeast of the first foreshock. The foreshock area expanded toward the trench axis with a velocity of several to several tens centimeters per second. The number of events per day increased daily, and the final size of the foreshock area was about 80 × 30 km. Eventually, the rupture of the mainshock started at the deepest point of the foreshock area. These observational facts are consistent with recent theoretical studies and laboratory experiments, in which foreshocks are regarded as the rupture of localized asperities in a broad weak zone where the nucleation of the large earthquake started.

Quick aftershock relocation of the 1994 Shikotan Earthquake and its fault planes

The 1994 Shikotan earthquake of Mw 8.2 occurred near the western Kurile trench where the Pacific plate is subducting beneath the North American plate. Although its mechanism is thrust‐type, it is not a typical low‐angle thrust event with a nodal plane parallel to the plate boundary that occurs at the plate boundary. In order to determine which of the two nodal planes of the main shock was the fault plane, we relocated the main shock and all aftershocks with M &gt; 5.3 using a modified joint hypocenter determination method. Earthquakes on the northwestern side of the aftershock area including the main shock are located along a plane dipping east‐southeastward with a dip of 70°. This plane is about 80 to 150 km long and 70 km wide. The main shock occurred at the north‐northeastern bottom of this plane, which is almost parallel to one of the two nodal planes of the main shock determined by Harvard University, which has a strike of N51°E and a dip of 76°. Thus we conclude that this plane is the fault plane, that the fault broke at the northeastern bottom of the fault plane and that the rupture propagated to the surface and also to the southeast. In addition to the aftershocks aligned with this fault plane, there is a secondary alignment, which is subparallel to the main fault plane and about 50 km east, where the largest aftershock of Mw 7.3 occurred on Oct. 9. Since several aftershocks occurred on this secondary fault plane on the same day as the main shock, it seems reasonable to suppose that this secondary fault plane was generated together with the main fault plane at the time of the main shock.