Physics of the Earth and Planetary Interiors最新文献

{"title":"Thermal and magnetic evolution of an Earth-like planet with a basal magma ocean","authors":"","doi":"10.1016/j.pepi.2024.107267","DOIUrl":"10.1016/j.pepi.2024.107267","url":null,"abstract":"<div><div>Earth's geodynamo has operated for over 3.5 billion years. The magnetic field is currently powered by thermocompositional convection in the outer core, which involves the release of light elements and latent heat as the inner core solidifies. However, since the inner core nucleated no more than 1.5 billion years ago, the early dynamo could not rely on these buoyancy sources. Given recent estimates of the thermal conductivity of the outer core, an alternative mechanism may be required to sustain the geodynamo prior to nucleation of the inner core. One possibility is a silicate dynamo operating in a long-lived basal magma ocean. Here, we investigate the structural, thermal, buoyancy, and magnetic evolution of an Earth-like terrestrial planet. Using modern equations of state and melting curves, we include a time-dependent parameterization of the compositional evolution of an iron-rich basal magma ocean. We combine an internal structure integration of the planet with energy budgets in a coupled core, basal magma ocean, and mantle system. We determine the thermocompositional convective stability of the core and the basal magma ocean, and assess their respective dynamo activity using entropy budgets and magnetic Reynolds numbers. Our conservative nominal model predicts a transient basal magma ocean dynamo followed by a core dynamo after 1 billion years. The model is sensitive to several parameters, including the initial temperature of the core-mantle boundary, the parameterization of mantle convection, the composition of the basal magma ocean, the radiogenic content of the planet, as well as convective velocity and magnetic scaling laws. We use the nominal model to constrain the range of basal magma ocean electrical conductivity and core thermal conductivity that sustain a dynamo. This highlights the importance of constraining the parameters and transport properties that influence planetary evolution using experiments and simulations conducted at pressure, temperature, and composition conditions found in planetary interior, in order to reduce model degeneracies.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2024-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142441256","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"3-D P-wave velocity structure of the upper mantle beneath eastern Indonesia from body wave tomography","authors":"","doi":"10.1016/j.pepi.2024.107266","DOIUrl":"10.1016/j.pepi.2024.107266","url":null,"abstract":"<div><div>Eastern Indonesia's tectonic setting is well known for its complexity and intense seismic activity. Controlled by several major and minor plates, including the Eurasian, Australian, and Pacific plates, this region is famous for its U-shaped subduction system beneath the Banda Arc. To better understand the architecture of the underlying structure in this region, we performed body-wave travel time tomography using ten years of catalog data provided by the Indonesian Agency for Meteorology, Climatology, and Geophysics. We utilize 9729 events in total, from which 46,446 P-wave arrival times were extracted. We used a double difference method to relocate the initial event catalog, which produced a pattern of seismicity consistent with a curved subduction system. Our tomographic model reveals a high velocity band between 90 and 240 km depth in the upper mantle, which is interpreted to be a concave dipping lithospheric slab that is parallel to the present-day Banda arc. Our results also show that lithosphere subducting from the north and south starts to collide at a depth of 300–350 km and becomes shallower further east. Apparent discontinuities in the high velocity band and a corresponding lack of seismicity supports the presence of a slab tear to the west of Seram. A dipping high velocity structure that is present from south to north beneath the island of Timor represents a subducting slab that dips more steeply beyond a depth of 150–200 km, which appears consistent with slab roll-back. Our tomographic model also shows evidence of back arc thrusting to the north of Sumbawa and Flores Islands in the form of a south-dipping higher velocity band at shallow depth. Furthermore, our tomographic models also reveal the possible presence of underthrust continental forearc in the form of a thin higher velocity anomaly that connects the backarc thrust and northward dipping lithosphere slab in the Timor area. Finally, a zone of low velocity above the higher velocity slab is clearly seen beneath Seram Island at a depth of ∼100 km and may represent a partial melting zone.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2024-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142428238","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Reinvestigating the Dufek Intrusion, through joint gravity and magnetic models","authors":"","doi":"10.1016/j.pepi.2024.107268","DOIUrl":"10.1016/j.pepi.2024.107268","url":null,"abstract":"<div><div>The Dufek layered mafic intrusion represents the only exposed, deep-seated, part of the Ferrar Large Igneous Province, which extends &gt;3500 km across Antarctica and into parts of Tasmania and New Zealand. The Dufek Intrusion is in a key position at the boundary between the Jurassic Weddell Sea Rift System and the East Antarctic Craton. It may have been a conduit for some of the Ferrar magmas, or a deep-seated equivalent to the shallower sills seen in other sectors of Antarctica. Although a significant intrusion, equivalent at least to the Stillwater complex in the USA, its true scale and geometry, along with the relative timing of emplacement is disputed. We present new 3D models of gravity and magnetic data which constrain the geometry of the intrusion, show how separate lobes of the intrusion are linked and identify a possible extension of the intrusion to the east. We also discuss the implications for how the intrusion may have been emplaced.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2024-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142428239","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The sensitivity of lowermost mantle anisotropy to past mantle convection","authors":"","doi":"10.1016/j.pepi.2024.107264","DOIUrl":"10.1016/j.pepi.2024.107264","url":null,"abstract":"<div><div>It is widely believed that seismic anisotropy in the lowermost mantle is caused by the flow-induced alignment of anisotropic crystals such as post-perovskite. What is unclear, however, is whether the anisotropy observations in the lowermost mantle hold information about past mantle flow, or if they only inform us about the present-day flow field. To investigate this, we compare the general and seismic anisotropy calculated using Earth-like mantle convection models where one has a time-varying flow, and another where the present-day flow is constant throughout time. To do this, we track a post-perovskite polycrystal through the flow fields and calculate texture development using the sampled strain rate and the visco-plastic self-consistent approach. We assume dominant slip on (001) and test the effect of the relative importance of this glide plane over others by using three different plasticity models with different efficiencies at developing texture. We compare the radial anisotropy parameters and the anisotropic components of the elastic tensors produced by the flow field test cases at the same location. We find, under all ease-of-texturing cases, the radial anisotropy is very similar (difference <span><math><mo>&lt;</mo><mn>2</mn><mo>%</mo></math></span>) in the majority of locations and in some regions, the difference can be very large (<span><math><mo>&gt;</mo><mn>10</mn><mo>%</mo></math></span>). The same is true when comparing the elastic tensors directly. Varying the ease-of-texture development in the crystal aggregate suggests that easier-to-texture material may hold a stronger signal from past flow than harder-to-texture material. Our results imply that broad-scale observations of seismic anisotropy such as those from seismic tomography, 1-D estimates and normal mode observations, will be mainly sensitive to present-day flow. Shear-wave splitting measurements, however, could hold information about past mantle flow. In general, mantle memory expressed in anisotropy may be dependent on path length in the post-perovskite stability field. Our work implies that, as knowledge of the exact causative mechanism of lowermost mantle anisotropy develops, we may be able to constrain both present-day and past mantle convection.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2024-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142328310","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Shock-induced phase transitions in siderite up to 90 GPa and implications for deep carbon cycle","authors":"","doi":"10.1016/j.pepi.2024.107265","DOIUrl":"10.1016/j.pepi.2024.107265","url":null,"abstract":"<div><div>The phase stability of carbonates under mantle conditions is important for understanding the global carbon cycle. In this study, the Hugoniot data of a natural siderite (FeCO₃) were measured up to 90 GPa using the plane-plate impact method. Two successive phase transitions were observed at 38–40 GPa and 65–69 GPa, respectively. In comparison with the static compression results, the first phase transition was identified as a spin transition, and the second is attributed to the self-redox reaction. The volume change during the self-redox transition is consistent with the reaction products of tetrairon orthocarbonate Fe₄C₃O₁₂ and diamond. Using the measured Hugoniot data, we estimated the density of Fe₄C₃O₁₂ along the lower mantle conditions and found it to be higher than the seismic values. Our results suggest siderite plays an important role in the deep carbon cycle.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2024-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142323620","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A potential deep geothermal reservoir in eastern Ladakh as inferred from the upper crustal geoelectric structure of the region","authors":"","doi":"10.1016/j.pepi.2024.107263","DOIUrl":"10.1016/j.pepi.2024.107263","url":null,"abstract":"<div><div>The Ladakh Himalaya is a repository of the evolutionary history of the India-Eurasia convergent plate margin. We present the results of a magnetotelluric (MT) study carried out in Eastern Ladakh along a 40-km-long profile traversing across various tectonic domains of this plate margin. We modeled the MT dataset by two-dimensional (2-D) and three-dimensional (3-D) inversion algorithms. The upper crustal geoelectric model obtained by 2-D inversion of distortion corrected and decomposed data of 18 sites shows an excellent match with the surface geology. In this model, the Indus Suture Zone (ISZ) appears as a steeply dipping contact and the Ladakh batholith is about 10 to 12 km thick. The model yields a prominent electrical conductor of ∼6 km diameter at 4 km depth beneath the Tso Morari Crystallines with an offshoot of a small conductor that rises upward along the ISZ. The geoelectrical model obtained by 3-D inversion is broadly consistent with the 2-D model but also reveals off-profile features and a connectivity of the shallow conductors with a widespread conductive zone at deeper level of the upper crust. In view of the presence of Puga and Chumathang hot springs towards west and Demchok hot springs towards east of our study region, we infer these conductors to be representing a potential major geothermal reservoir system connected to the widespread deeper conductive zone of partial melts, which extends from the southern Tibet to the eastern Ladakh region.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2024-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142323619","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"On the relationship between paleomagnetic secular variation and excursions – Records from MIS 11 and 12 – ODP Leg 172, western North Atlantic Ocean","authors":"","doi":"10.1016/j.pepi.2024.107249","DOIUrl":"10.1016/j.pepi.2024.107249","url":null,"abstract":"<div><p>This study has developed paleomagnetic secular variation (PSV) records from Sites 1060, 1061, 1062, and 1063 (ODP Leg 172) from the western North Atlantic Ocean during MIS 11–12 (374–478 ka). We have identified 46 inclination features and 49 declination features that can be correlated among the records. We have also developed relative paleointensity records and identified 13 paleointensity features that can be correlated among them. These features can also be dated using the oxygen-isotope dated Global relative-paleointensity record PISO-1500 of Channell et al. (2009). There is one excursion located in these four records. We use the name Levantine/Bermuda Excursion developed elsewhere by Ryan (1972) and Channell et al. (2017). The Excursion occurred at 408 ± 4 ka. The excursion is recorded at Sites 1061, 1062, and 1063. The most detailed excursion records occur at Site 1062 where we have both shipboard PSV records and one u-channel PSV record of the excursion. The excursion has two intervals of excursional directions, one short interval (∼I ky) followed by a long interval (∼5 ky). Both intervals have counter-clockwise looping of the excursional directions and the excursion is considered to be a Class I Excursion (Lund et al., 2005). Statistical study of the PSV records after removal of the excursion directions has identified two characteristics of the ‘normal’ PSV. The first feature is a long-term (&gt;10⁴ yrs) deviation in inclination and declination averages from the overall site averages. These deviations suggest some type on long-term memory in the regional dynamo process. The second feature is the variation in PSV angular dispersion (a measure of directional variability). The angular dispersion is quite low (∼12°) for most of the 374–478 ka interval. But, there is a short (∼8 ky) interval with angular dispersion more than double the amplitude (∼25°-30°). This interval has a sharp (&lt;3 ky) onset and termination, This interval contains the Levantine/Bermuda Excursion. Such high-angular dispersion intervals with associated excursions and low paleointensity appear to be regular distinctive features of the Brunhes Chron PSV.</p></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142272088","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Wudalianchi volcanism and mantle dynamics in Northeast China: New insight from Pn and Sn tomography","authors":"","doi":"10.1016/j.pepi.2024.107260","DOIUrl":"10.1016/j.pepi.2024.107260","url":null,"abstract":"<div><div>We determine new tomographic models of Pn anisotropic velocity and Sn isotropic velocity in and around the Wudalianchi volcanic area by inverting high-quality Pn and Sn arrival times manually picked from waveforms recorded at the newly deployed high-dense WAVESArray portable seismic stations. Our high-resolution Pn and Sn velocity models reveal strong lateral heterogeneities in the uppermost mantle under the study region. The average Pn and Sn velocities in the uppermost mantle are 8.2 and 4.5 km/s, respectively. Both Pn and Sn velocity models exhibit obvious low-velocity (low-V) anomalies under the Wudalianchi and Keluo volcanoes, whereas under the Songliao basin distinct high-velocity (high-V) zones are revealed. In particular, our Pn model reveals two separate low-V anomalies under the Nuominhe and Halaha volcanic groups, suggesting that they have different deep origins. A large-scale L-shaped low-V zone exists under the Keluo, Wudalianchi, Erkeshan, and Xunke volcanoes, characterized by Pn-wave fast propagation directions (FPDs) parallel with the low-V zone, suggesting that these volcanoes may have the same deep origin. Furthermore, southeast-opened U-shaped Pn FPDs exist around the Wudalianchi volcano, whereas NE-SW FPDs appear under the Great Xing'an range, which are generally consistent with SKS splitting measurements. This feature may reflect lithosphere-asthenosphere coupling beneath the Wudalianchi volcano associated with horizontal flows in the big mantle wedge and compressional tectonics under the Great Xing'an range. These results shed new lights on the Wudalianchi volcanism and mantle dynamics beneath Northeast China.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142310256","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Randomization of the Earth's magnetic field driven by magnetic helicity","authors":"","doi":"10.1016/j.pepi.2024.107250","DOIUrl":"10.1016/j.pepi.2024.107250","url":null,"abstract":"<div><p>It is shown, using results of numerical simulations and geomagnetic observations, that the spatial and temporal randomization of the Earth's global and local magnetic fields is driven by magnetic helicity (an ideal magnetohydrodynamic invariant). In the frames of the distributed chaos notion, the magnetic helicity determines the degree of magnetic field randomization and the results of numerical simulations are in quantitative agreement with the geophysical observations despite the considerable differences in the scales and physical parameters.</p></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142272015","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Space and time distribution of seismic source energy at Campi Flegrei, Italy through the last unrest phase (1.1.2000–31.12.2023)","authors":"","doi":"10.1016/j.pepi.2024.107258","DOIUrl":"10.1016/j.pepi.2024.107258","url":null,"abstract":"&lt;div&gt;&lt;p&gt;We describe the space-time pattern of seismicity occurring on Campi Flegrei Caldera (CFC), Italy, where ground deformations and seismicity represent the drivers of its current bradyseismic crisis, well known and extensively studied at an international level. In detail we consider the seismicity in the time interval starting on 1.1.2000 and ending on 31.12.2023. We revise the statistics of the earthquake occurrence, focusing at possible precursory time changes of the b-parameter of the Gutenberg and Richter (G&amp;R &lt;span&gt;&lt;math&gt;&lt;mi&gt;b&lt;/mi&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mi&gt;value&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt;) distribution and at the time distribution of the total seismic moment inside any swarm. To estimate the G&amp;R &lt;span&gt;&lt;math&gt;&lt;mi&gt;b&lt;/mi&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mi&gt;value&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; we use a Monte Carlo method instead of the ordinary Least Squares or Maximum likelihood methods, to easily measure the uncertainty on the &lt;span&gt;&lt;math&gt;&lt;mi&gt;b&lt;/mi&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mi&gt;value&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; taking into account uncertainties on the magnitude estimates. Results show that G&amp;R &lt;span&gt;&lt;math&gt;&lt;mi&gt;a&lt;/mi&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mi&gt;value&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; and &lt;span&gt;&lt;math&gt;&lt;mi&gt;b&lt;/mi&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mi&gt;value&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; calculated for cumulative and discrete distributions of &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mi&gt;M&lt;/mi&gt;&lt;mi&gt;w&lt;/mi&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;, the moment-magnitude, and &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mi&gt;M&lt;/mi&gt;&lt;mi&gt;d&lt;/mi&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;, the so-called duration-magnitude, are the same inside the uncertainties; &lt;span&gt;&lt;math&gt;&lt;mi&gt;a&lt;/mi&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mi&gt;value&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; and &lt;span&gt;&lt;math&gt;&lt;mi&gt;b&lt;/mi&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mi&gt;value&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; for &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mi&gt;M&lt;/mi&gt;&lt;mi&gt;d&lt;/mi&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; are significantly different from the same parameters estimated for &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mi&gt;M&lt;/mi&gt;&lt;mi&gt;w&lt;/mi&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;, being &lt;span&gt;&lt;math&gt;&lt;mi&gt;b&lt;/mi&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mi&gt;value&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; for &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mi&gt;M&lt;/mi&gt;&lt;mi&gt;w&lt;/mi&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; close to the value of 1.0 and &lt;span&gt;&lt;math&gt;&lt;mi&gt;b&lt;/mi&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mi&gt;value&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; for &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mi&gt;M&lt;/mi&gt;&lt;mi&gt;d&lt;/mi&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; close to 0.8. The “bounded” G&amp;R distribution fits the data yielding &lt;span&gt;&lt;math&gt;&lt;mi&gt;a&lt;/mi&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mi&gt;value&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; and &lt;span&gt;&lt;math&gt;&lt;mi&gt;b&lt;/mi&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mi&gt;value&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; close to those for the unbounded distribution. The mean annual rate of exceedance, calculated for the entire catalogue, results to be 0.033&lt;span&gt;&lt;math&gt;&lt;mo&gt;±&lt;/mo&gt;&lt;mn&gt;0.015&lt;/mn&gt;&lt;/math&gt;&lt;/span&gt; (years&lt;sup&gt;−1&lt;/sup&gt;) corresponding to a return period of &lt;span&gt;&lt;math&gt;&lt;mn&gt;30&lt;/mn&gt;&lt;mo&gt;±&lt;/mo&gt;&lt;mn&gt;14&lt;/mn&gt;&lt;/math&gt;&lt;/span&gt; years for &lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mi&gt;M&lt;/mi&gt;&lt;mi&gt;w&lt;/mi&gt;&lt;/msub&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mn&gt;4.5&lt;/mn&gt;&lt;/math&gt;&lt;/span&gt;. The time dependence of G&amp;R b-parameter show a &lt;span&gt;&lt;math&gt;&lt;mi&gt;b&lt;/mi&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mi&gt;value&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; time pattern characterized by variations slightly outside 1-&lt;span&gt;&lt;math&gt;&lt;mi&gt;σ&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; uncertainty bar, tending to the value of 1 approaching present. As evidenced by several past studies, earthquakes in CFC occur in space-t","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S003192012400116X/pdfft?md5=a859af686a6ea4310c7c90813110214b&pid=1-s2.0-S003192012400116X-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142272089","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}