Automated,high time-resolution measurements of SO<Subscript>2</Subscript> flux at Soufrière Hills Volcano,Montserrat

We report here the first results from an automated, telemetered UV scanning spectrometer system for monitoring SO ₂ emission rates at Soufrière Hills Volcano, Montserrat. Two spectrometers receive light by way of a motor-driven stepping prism and telescope in order to make vertical scans of the volcanic plume. Spectral data from these spectrometers, situated 2,800 m apart and 4,500 m from the volcano, are relayed back to the observatory every 4–5 s via radio modems. A full scan of the plume is accomplished every 1–6 min by the (time-synchronised) spectrometers and a SO ₂ emission rate is calculated using the SO ₂ slant concentrations, scan angles and plume speeds estimated from the wind speed from a telemetered weather station near to the volcano. The plume's position and dimensions are calculated using the angular data from the two spectrometers. The plume height varies significantly diurnally and seasonally and is important in order to minimise the error on SO ₂ emission rates. The new scanning system (Scanspec) provides SO ₂ emission rates from 08:00 to 16:00 h local time every day. Preliminary results highlight a number of features of the SO ₂ time series and plume dynamics and give our first indications of the errors and limits of detection of this system. SO ₂ emission rates vary widely on all time scales (minutes, days, months). This new system has already provided the first real and consistent indication that SO ₂ emission rates vary on a minutes to hours basis, which can be correlated with volcanic activity (for example, rockfall and pyroclastic flow activity). It is anticipated that this system at Soufrière Hills will yield information on shallow processes occurring on short time scales (periods of minutes to hours) as well as deep processes relating to magma supply rates, which will be associated with longer wavelength SO ₂ signals of weeks to months.     

Ionospheric <Emphasis Type="Italic">N</Emphasis><Subscript>e</Subscript> disturbances before 2007 Pu’er,Yunnan, China,earthquake

Selecting three half orbits near the epicenter of Pu’er earthquake, we analyzed the N_e data recorded in their revisited orbits during a year before this earthquake, and extracted N_e precursors. The results show that: ① There are significant seasonal variations of ionospheric N_e in night time, which exhibit different shapes respectively in four seasons; ② There are three main shapes of N_e: single-peak, saddle-shaped and even-shaped, all of which may occur in four seasons, but each season with its typical shape relatively; ③ Spatial images of N_e showed high values near the epicenter in 30 days before the earthquake, and there is a good correlation between anomaly and distribution of earthquake in space and time, which reflects that these spatial anomalies were indeed concerned with the earthquake; ④ There shows a certain similarity of the N_e curves among revisited orbits, which can provide background information for distinguishing and identification of seismic anomaly.     

Apparent downwind depletion of volcanic SO<Subscript>2</Subscript> flux—lessons from Masaya Volcano,Nicaragua

A series of 707 measurements at Masaya in 2005, 2006, and 2007 reveals that SO₂ emissions 15km downwind of the active vent appear to be ~33% to ~50% less than those measured only 5km from the vent. Measurements from this and previous studies indicate that dry deposition of sulfur from the plume and conversion of SO₂ to sulfate aerosols within the plume each may amount to a maximum of 10% loss, and are not sufficient to account for the larger apparent loss measured. However, the SO₂ measurement site 15km downwind is located on a ridge over which local trade winds, and the entrained plume, accelerate. Greater wind speeds cause localized dilution of the plume along the axis of propagation. The lower concentrations of SO₂ measured on the ridge therefore lead to calculations of lower fluxes when calculated at the same plume speed as measurements from only 5km downwind, and is responsible for the apparent loss of SO₂. Due to the importance of SO₂ emission rates with respect to hazard mitigation, petrologic studies, and sulfur budget calculations, measured fluxes of SO₂ must be as accurate as possible. Future campaigns to measure SO₂ flux at Masaya and similar volcanoes will require individual plume speed measurements to be taken at each flux measurement site to compensate for dilution and subsequent calculation of lower fluxes. This study highlights the importance of a comprehensive understanding of a volcano’s interaction with its surroundings, especially for low, boundary layer volcanoes.     

High Frequency PKKP<Subscript>BC</Subscript> Around 2.5 Hz Recorded Globally

Anomalous high frequency PKKP_BC signals (displaying a large amount of energy around 2.5 Hz), recorded globally for deep and intermediate depth earthquakes, are compared to PKKP_AB signals. The attenuation difference t_\textAB^* - t_\textBC^* t_{\text{AB}}^{*} - t_{\text{BC}}^{*} is evaluated from spectral amplitudes in the range 96–111°, being approximately twice the results provided by full-wave theory and PREM (with no low Q_μ zone in the lowermost mantle and a nearly infinite Q_K in the outer core). Most ray paths for such recordings are piercing the D″ region in the proximity of regions where ultra-low velocity zones (ULVZ) have been previously reported beneath the North Atlantic Ocean, the Southwest Pacific and the southwestern part of South America. If BC amplitudes around 2.5 Hz and at low frequencies (0.5–1.5 Hz) are comparable, the observed attenuation difference (in the frequency range 0.2–2.5 Hz) is small (around 0.25 s) and close to the PREM value. The particle motion of the high-frequency PKKP_BC at 2.5 Hz is quite similar to that of the raw recording, suggesting a deep source. An explanation for this might be scattering of the BC branch in some very restricted areas of the lowermost mantle. Alternately, the presence of a thin layer with high attenuation in the D″ region would most likely be associated with either the ultra-low velocity zone (ULVZ) or light sediments on the underside of the core-mantle boundary (CMB). Correlated to other methods to investigate the lowermost mantle, the high-frequency PKKP_BC can be used to map lateral variations of attenuation above the CMB, possibly associated with the boundary of the superplumes, especially when PKKP_AB is observed.     

Bias,variance and computational properties of Kijko’s estimators of the upper limit of magnitude distribution,M<Subscript>max</Subscript>

It is often assumed in probabilistic seismic hazard analysis that the magnitude distribution has an upper limit M _max, which indicates a limitation on event size in specific seismogeneic conditions. Accurate estimation of M _max from an earthquake catalog is a matter of utmost importance. We compare bias, dispersion and computational properties of four popular M _max estimators, introduced by Kijko and others (e.g., Kijko and Sellevoll 1989, Kijko and Graham 1998, Kijko 2004) and we recommend the ones which can be the most fruitful in practical applications. We provide nomograms for evaluation of bias and standard deviation of the recommended estimators for combinations of sample sizes and distribution parameters. We suggest to use the bias nomograms to correct the M _max estimates. The nomograms of standard deviation can be used to determine minimum sample size for a required accuracy of M _max.     

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.     

IR band of O<Subscript>2</Subscript> at 1.27 μm as the tracer of O<Subscript>3</Subscript> in the mesosphere and lower thermosphere: Correction of the method

The problem of systematic overestimation (20–50%) of the retrieved ozone concentrations in the altitude range of 60–80 km in the TIMED–SABER satellite experiment in the daytime has been solved. The reason for overestimation is the neglect of the electronic vibrational kinetics of photolysis products of ozone and molecular oxygen O₂(b¹Σ_g ⁺, ν) and O₂(a¹Δ_g, ν). The IR emission band of O₂(a¹Δ_g, ν = 0) at 1.27 μm can be correctly used in remote sensing in order to obtain the ozone altitude profile in the altitude range of 50–88 km only with the use of a complete model of electronic vibrational kinetics of O₂ and O₃ photolysis products (YM2011) in the Earth’s mesosphere and lower thermosphere. Alternative ozone tracers have been considered, and an optimum tracer in the altitude range of 50–100 km such as O₂(b¹Σ_g ⁺, ν = 1) molecule emissions has been proposed.     

CO<Subscript>2</Subscript> and He degassing at El Chichón volcano,Chiapas, Mexico: gas flux,origin and relationship with local and regional tectonics

During 2007–2008, three CO₂ flux surveys were performed on El Chichón volcanic lake, Chiapas, Mexico, with an additional survey in April 2008 covering the entire crater floor (including the lake). The mean CO₂ flux calculated by sequential Gaussian simulation from the lake was 1,190 (March 2007), 730 (December 2007) and 1,134 g m⁻² day⁻¹ (April 2008) with total emission rates of 164 ± 9.5 (March 2007), 59 ± 2.5 (December 2007) and 109 ± 6.6 t day⁻¹ (April 2008). The mean CO₂ flux estimated from the entire crater floor area was 1,102 g m⁻² day⁻¹ for April 2008 with a total emission rate of 144 ± 5.9 t day⁻¹. Significant change in CO₂ flux was not detected during the period of survey, and the mapping of the CO₂ flux highlighted lineaments reflecting the main local and regional tectonic patterns. The ³He/⁴He ratio (as high as 8.1 R _A) for gases in the El Chichón crater is generally higher than those observed at the neighbouring Transmexican Volcanic Belt and the Central American Volcanic Arc. The CO₂/³He ratios for the high ³He/⁴He gases tend to have the MORB-like values (1.41 × 10⁹), and the CO₂/³He ratios for the lower ³He/⁴He gases fall within the range for the arc-type gases. The high ³He/⁴He ratios, the MORB-like CO₂/³He ratios for the high ³He/⁴He gases and high proportion of MORB-CO₂ (M = 25 ±15%) at El Chichón indicate a greater depth for the generation of magma when compared to typical arc volcanoes.     

Hovsgol earthquake 5 December 2014, <Emphasis Type="Italic">M</Emphasis><Subscript>W</Subscript> = 4.9: seismic and acoustic effects

A moderate shallow earthquake occurred on 5 December 2014 (M _W = 4.9) in the north of Lake Hovsgol (northern Mongolia). The infrasonic signal with duration 140 s was recorded for this earthquake by the “Tory” infrasound array (Institute of Solar-Terrestrial Physics of the Siberian Branch of the Russian Academy of Science, Russia). Source parameters of the earthquake (seismic moment, geometrical sizes, displacement amplitudes in the focus) were determined using spectral analysis of direct body P and S waves. The spectral analysis of seismograms and amplitude variations of the surface waves allows to determine the effect of the propagation of the rupture in the earthquake focus, the azimuth of the rupture propagation direction and the velocity of displacement in the earthquake focus. The results of modelling of the surface displacements caused by the Hovsgol earthquake and high effective velocity of propagation of infrasound signal (~ 625 m/s) indicate that its occurrence is not caused by the downward movement of the Earth’s surface in the epicentral region but by the effect of the secondary source. The position of the secondary source of infrasound signal is defined on the northern slopes of the Khamar-Daban ridge according to the data on the azimuth and time of arrival of acoustic wave at the Tory station. The interaction of surface waves with the regional topography is proposed as the most probable mechanism of formation of the infrasound signal.     

The Tolud Burst of Seismicity and the Earthquake of November 30, 2012 (<Emphasis Type="Italic">M</Emphasis><Subscript>C</Subscript> = 5.4, <Emphasis Type="Italic">M</Emphasis><Subscript>W</Subscript> = 4.8) that Accompanied the Start of the 2012‒2013 Tolbachik Eruption

This paper reports a study of the Tolud earthquake sequence; the sequence was a burst of shallow seismicity between November 28 and December 7, 2012; it accompanied the initial phase in the Tolbachik Fissure Eruption of 2012?2013. The largest earthquake (the Tolud earthquake of November 30, 2012, to be referred to as the Tolud Earthquake in what follows, with K_S = 11.3, M_L = 4.9, M_C = 5.4, and M_W = 4.8) is one of the five larger seismic events that have been recorded at depths shallower than 10 km beneath the entire Klyuchevskoi Volcanic Cluster in 1961?2015. It was found that the Tolud earthquake sequence was the foreshock–aftershock process of the Tolud Earthquake. This is one of the larger seismicity episodes ever to have occurred in the volcanic areas of Kamchatka. Data of the Kamchatka seismic stations were used to compute some parameters for the Tolud Earthquake and its largest (M_L = 4.3) aftershock; the parameters include the source parameters and mechanisms, and the moment magnitudes, since no information on these is available at the world seismological data centers. The focal mechanisms for the Tolud Earthquake and for its aftershock are consistent with seismic ruptures at a tension fault in the rift zone. Instrumental data were used to estimate the intensity of shaking due to the Tolud Earthquake. We discuss the sequence of events that was a signature of the time-dependent seismic and volcanic activity that took place in the Tolbachik zone in late November 2012 and terminated in the Tolud burst of seismicity. Based on the current ideas of the tectonics and magma sources for the Tolbachik volcanic zone, we discuss possible causes of these earthquakes.     

Structural analysis and interpretation of the surface deformation associated with the Ning’er,Yunnan Province,China <Emphasis Type="Italic">M</Emphasis><Subscript>S</Subscript>6.4 earthquake of June 3, 2007

The seismogenic fault and the dynamic mechanism of the Ning’er, Yunnan Province M_S6.4 earthquake of June 3, 2007 are studied on the basis of the observation data of the surface fissures, sand blow and water eruption, landslide and collapse associated with the earthquake, incorporating with the data of geologic structures, focal mechanism solutions and aftershock distribution for the earthquake area. The observation of the surface fissures reveals that the Banhai segment of the NW-trending Ning’er fault is dominated by right-lateral strike-slip, while the NNE-trending fault is dominated by left-lateral strike-slip. The seismo-geologic hazards are concentrated mainly within a 330°-extending zone of 13.5 km in length and 4 km in width. The major axis of the isoseismal is also oriented in 330° direction, and the major axis of the seismic intensity VIII area is 13.5 km long. The focal mechanism solutions indicate that the NW-trending nodal plane of the Ning’er M_S6.4 earthquake is dominated by right-lateral slip, while the NE-trending nodal plane is dominated by left-lateral slip. The preferred distribution orientation of the aftershocks of M_S≥2 is 330°, and the focal depths are within the range of 3～12 km, predominantly within 3～10 km. The distribution of the aftershocks is consistent with the distribution zone of the seismo-geologic hazards. All the above-mentioned data indicate that the Banhai segment of the Ning’er fault is the seismogenic fault of this earthquake. Moreover, the driving force of the Ning’er earthquake is discussed in the light of the active block theory. It is believed that the northward pushing of the Indian plate has caused the eastward slipping of the Qinghai-Tibetan Plateau, which has been transformed into the southeastern-southernward squeezing of the southwest Yunnan region. As a result, the NW-trending faults in the vicinity of the Ning’er area are dominated by right-lateral strike-slip, while the NE-trending faults are dominated by left-lateral strike-slip. This tectonic framework might be the main cause of the frequent occurrence of M_S6.0～6.9 earthquakes in the area.     

Simulating CO<Subscript>2</Subscript> transport into the ocean from a CO<Subscript>2</Subscript> lake at the seafloor using a <Emphasis Type="Italic">z</Emphasis>- and a <Emphasis Type="Italic">σ</Emphasis>-coordinate model

The ocean takes up approximately 2 GT carbon per year due to the enhanced CO₂ concentrations in the atmosphere. Several options have been suggested in order to reduce the emissions of CO₂ into the atmosphere, and among these are CO₂ storage in the deep ocean. Topographic effects of dissolution and transport from a CO₂ lake located at 3,000-m depth have been studied using the z-coordinate model Massachusetts Institute of Technology general circulation model (MITgcm) and the σ-coordinate model Bergen ocean model (BOM). Both models have been coupled with the general ocean turbulence model (GOTM) in order to account for vertical subgrid processes. The chosen vertical turbulence mixing scheme includes the damping effect from stable stratification on the turbulence intensity. Three different topographic scenarios are presented: a flat bottom and the CO₂ lake placed within a trench with depths of 10 and 20 m. The flat case scenario gives good correlation with previous numerical studies of dissolution from a CO₂ lake. When topography is introduced, it is shown that the z-coordinate model and the σ-coordinate model give different circulation patterns in the trench. This leads to different dissolution rates, 0.1 μmol cm^− 2 s^− 1 for the scenario of a 20-m-deep trench using BOM and 0.005–0.02 μmol cm^− 2 s^− 1 for the same scenario using the MITgcm. The study is also relevant for leakages of CO₂ stored in geological formations and to the ocean.     

The <Emphasis Type="Italic">M</Emphasis><Subscript>w</Subscript> 3.1–4.7 earthquakes in the southern Baltic Sea and adjacent areas in 2000, 2001 and 2004

The area south and east of the Baltic Sea has very minor seismic activity. However, occasional events occur as illustrated by four events in recent years, which are analysed in this study: near Wittenburg, Germany, on May 19, 2000, M _w = 3.1, near Rostock, Germany, on July 21, 2001, M _w = 3.4 and in the Kaliningrad area, Russia, two events on September 21, 2004 with M _w = 4.6 and 4.7. Locations, magnitudes (M _L and M _w) and focal mechanisms were determined for the two events in Germany. Synthetic modeling resulted in a well-confined focal depth for the Kaliningrad events. The inversion of macroseismic observations provided simultaneous solutions of the location, focal depth and epicentral intensity. The maximum horizontal compressive stress orientations obtained from focal mechanism solutions, approximately N–S for the two German events and NNW–SSE for the Kaliningrad events, show a good agreement with the regionally oriented crustal stress field.     

Comparison of SPT and <Emphasis Type="Italic">V</Emphasis><Subscript>s</Subscript>-based liquefaction analyses: a case study in Erciş (Van,Turkey)

Liquefaction which is one of the most destructive ground deformations occurs during an earthquake in saturated or partially saturated silty and sandy soils, which may cause serious damages such as settlement and tilting of structures due to shear strength loss of soils. Standard (SPT) and cone (CPT) penetration tests as well as the shear wave velocity (V _s)-based methods are commonly used for the determination of liquefaction potential. In this research, it was aimed to compare the SPT and V _s-based liquefaction analysis methods by generating different earthquake scenarios. Accordingly, the Erci? residential area, which was mostly affected by the 2011 Van earthquake (M _w = 7.1), was chosen as the model site. Erci? (Van, Turkey) and its surroundings settle on an alluvial plain which consists of silty and sandy layers with shallow groundwater level. Moreover, Çald?ran, Erci?–Kocap?nar and Van Fault Zones are the major seismic sources of the region which have a significant potential of producing large magnitude earthquakes. After liquefaction assessments, the liquefaction potential in the western part of the region and in the coastal regions nearby the Lake Van is found to be higher than the other locations. Thus, it can be stated that the soil tightness and groundwater level dominantly control the liquefaction potential. In addition, the lateral spreading and sand boiling spots observed after the 23rd October 2011 Van earthquake overlap the scenario boundaries predicted in this study. Eventually, the use of V _s-based liquefaction analysis in collaboration with the SPT results is quite advantageous to assess the rate of liquefaction in a specific area.     

Strong motion characteristics of the <Emphasis Type="Italic">M</Emphasis><Subscript>w</Subscript> 6.6 Lushan earthquake,Sichuan, China — an insight into the spatial difference of a typical thrust fault earthquake

Near-field strong ground motions are useful for engineering seismology studies and seismic design, but dense observation networks of damaging earthquakes are still rare. In this study, based on the strong-motion data from the M w 6.6 Lushan earthquake, the ground motion parameters in different spatial regions are systematically analyzed, and the contributions from different effects, like the hanging-wall effect, directivity effect, and attenuation effect are separated to the extent possible. Different engineering parameters from the observed ground motions are compared with the local design response spectra and a new attenuation relation of Western China. General results indicate that the high frequency ground motion, like the peak ground acceleration, on two sides of the fault plane is sensitive to the hanging-wall effect, whereas the low frequency ground motion, like the long period spectral acceleration, in the rupture propagation direction is affected by the directivity effect. Moreover, although the M w 6.6 Lushan earthquake is not a large magnitude event, the spatial difference of ground motion is still obvious; thus, for a thrust faulting earthquake, in addition to the hanging effect, the directivity effect should also be considered.     

A simulation–optimization modeling approach for watershed-scale agricultural N<Subscript>2</Subscript>O emission mitigation under multi-level uncertainties

In this research, an integrated simulation–optimization modeling approach (ISOMA) was developed for supporting agricultural N₂O emission mitigation at the watershed scale. This approach can successfully combine soil N₂O emission simulation and the consequential mitigation management within a general modeling framework. Also, uncertainties associated with the key soil parameter can be effectively reflected and addressed through adoption of Monte Carlo analysis for the simulation results. The Monte Carlo simulated results were then used to generate fuzzy membership functions that can be consequentially used for emission mitigation management, reflecting the combined uncertainties for N₂O emission simulation and mitigation management. The developed ISOMA was then applied to a reservoir watershed in Miyun county of Beijing municipality. In the studying watershed, the simulation model was calibrated and verified. Then, N₂O emission from multiple agricultural land-use patterns were predicted. The amounts of N₂O emission of four land use patterns (i.e., cash tree, orchard, cropland, and natural forest) were (536.9, 590.8, 653.1), (237.7, 254.4, 275.9), (79.5, 100.7, 105.1), (33.0, 47.3, 61.1) kg CO₂ eq ha^?1 year^?1, respectively. Two scenarios (i.e., G₁ and G₂) were set up according to development priorities of local economy and society. Meanwhile, multiple credibility levels were considered according to the risk of N₂O emission. The land use patterns could be adjusted according to solutions of ISOMA. The developed methods could help regional manager choose various production patterns with cost-effective agriculture N₂O emission management schemes in the Miyun reservoir watershed. The manager also can obtain deeply insights into the tradeoffs between agricultural benefits and system reliabilities.     

Methods and technique of measurements of ρ<Subscript><Emphasis Type="Italic">k</Emphasis></Subscript> variations by GEOMES-R6 device

Upgrading of the electrical resistance variometer GEOMES-R6 of the Institute of Geophysics of the Poland Academy of Sciences, with enhancement of functional capabilities of the GEOMES assemblage for its application in laboratory measurements on rock samples, has been carried out. The assemblage operation principle, specifications, and theory of operation are given. Results of the assemblage test at measurements on marble sample and concrete model are presented. It is shown that the installation allows long-duration registration of variations of the value ρ _k on high-ohmic samples.     

Quantitatively distinguishing sediments from the Yangtze River and the Yellow River using δ Eu<Subscript>N</Subscript>-ΣREEs plot

Sediment samples were collected from the lower channel of the Yangtze River and the Yellow River and the contents of rare earth elements (REEs) were measured. In addition, some historical REEs data were collected from published literatures. Based on the δ Eu_N-ΣREEs plot, a clear boundary was found between the sediments from the two rivers. The boundary can be described as an orthogonal polynomial equation by ordinary linear regression with sediments from the Yangtze River located above the curve and sediments from the Yellow River located below the curve. To validate this method, the REEs contents of sediments collected from the estuaries of the Yangtze River and the Yellow River were measured. In addition, the REEs data of sediment Core 255 from the Yangtze River and Core YA01 from the Yellow River were collected. Results show that the samples from the Yangtze River estuary and Core 255 almost are above the curve and most samples from the Yellow River estuary and Core YA01 are below the curve in the δEu_N-ΣREEs plot. The plot and the regression equation can be used to distinguish sediments from the Yangtze River and the Yellow River intuitively and quantitatively, and to trace the sediment provenance of the eastern seas of China. The difference between the sediments from two rivers in the δEu_N-ΣREEs plot is caused by different mineral compositions and regional climate patterns of the source areas. The relationship between δEu_N and ΣREEs is changed little during the transport from the source area to the river, and from river to the sea. Thus the original information on mineral compositions and climate of the source area was preserved. Supported by National Natural Science Foundation of China (Grant Nos. 40506016, 40576032, and 90411014)     

New characteristics of intensity assessment of Sichuan Lushan “4.20” <Emphasis Type="Italic">M</Emphasis><Subscript>s</Subscript>7.0 earthquake

The post-earthquake rapid accurate assessment of macro influence of seismic ground motion is of significance for earthquake emergency relief, post-earthquake reconstruction and scientific research. The seismic intensity distribution map released by the Lushan earthquake field team of the China Earthquake Administration (CEA) five days after the strong earthquake (M7.0) occurred in Lushan County of Sichuan Ya’an City at 8:02 on April 20, 2013 provides a scientific basis for emergency relief, economic loss assessment and post-earthquake reconstruction. In this paper, the means for blind estimation of macroscopic intensity, field estimation of macro intensity, and review of intensity, as well as corresponding problems are discussed in detail, and the intensity distribution characteristics of the Lushan “4.20” M7.0 earthquake and its influential factors are analyzed, providing a reference for future seismic intensity assessments.