Detailed Investigation of the Foreshock Sequence of the 2010 Mw7.2 El Mayor‐Cucapah Earthquake

Foreshocks can provide valuable information about possible nucleation process of a mainshock. However, their physical mechanisms are still under debate. In this study, we present a comprehensive analysis of the earthquake sequence preceding the 2010 Mw7.2 El Mayor‐Cucapah mainshock, including waveform detection of missing smaller events, relative relocation, and source parameter analysis. Based on a template matching method, we find a tenfold increase in the number of earthquakes than reported in the Southern California Seismic Network catalog. The entire sequence exhibits nearly continuous episodes of foreshocks that can be loosely separated into two active clusters. Relocated foreshocks show several seismicity streaks at depth, with a consistently active cluster at depths between 14 and 16 km where the mainshock was nucleated. Stress drop measurements from a spectral ratio approach based on empirical Green’s functions show a range between 3.8 and 41.7 MPa with a median of 13.0 MPa and no clear temporal variations. The relocation results, together with the source patches estimated from earthquake corner frequencies, revealed a migration front toward the mainshock hypocenter within last 8 hr and a chain of active burst immediately 6 min prior to the mainshock. Our results support combined effects of aseismic slip and cascading failure on the evolution of foreshocks.Plain Language SummaryThe 2010 Mw7.2 El Mayor‐Cucapah (EMC) earthquake was preceded by a prominent sequence of foreshocks starting ~21 days before the mainshock. Several methods based on the similarities of waveforms are applied to obtain spatiotemporal evolution of foreshocks. Ten times more events are found from a template matching method when compared to the SCSN catalog. The refined relative locations reveal two main active clusters in time, as well as two spatial patches with a shallower one to the north of the mainshock epicenter. The depth distribution indicates several linear lines of seismicity, with a consistently active cluster at depths of 14–16 km where mainshock started. An active cluster of foreshocks occurred in the last 6 min. They likely altered the stress state near the hypocenter and ultimately triggered the mainshock. Our analysis indicates that both aseismic slip and cascade triggering processes occurred and contributed to the eventual triggering of the EMC mainshock.Key PointsA waveform matching technique leads to tenfold increase in the number of foreshocks when compared with the SCSN catalogWe resolve the corner frequency of 20 foreshocks using the detected events as empirical Green’s functionsThe relocated catalog and estimated source patches reveal effects of both aseismic slip and cascading stress transferPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155988/1/jgrb54188.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155988/2/jgrb54188_am.pd

Simulation study of spatio-temporal correlations of earthquakes as a stick-slip frictional instability

Spatio-temporal correlations of earthquakes are studied numerically on the basis of the one-dimensional spring-block (Burridge-Knopoff) model. As large events approach, the frequency of smaller events gradually increases, while, just before the mainshock, it is dramatically suppressed in a close vicinity of the epicenter of the upcoming mainshock, a phenomenon closely resembling the ``Mogi doughnut'

The Influence of Viscoelastic Crustal Rheologies on Volcanic Ground Deformation: Insights from Models of Pressure and Volume Change

This is the final version. Avaialble on open access from Wiley via the DOI in this recordInelastic rheological behaviour, such as viscoelasticity, is increasingly utilised in the modelling of volcanic ground deformation, as elevated thermal regimes induced by magmatic systems may necessitate the use of a mechanical model containing a component of time-dependent viscous behaviour. For the modelling of a given amplitude and footprint of ground deformation, incorporating a viscoelastic regime has been shown to reduce the magma reservoir overpressure requirements suggested by elastic models. This phenomenon, however, is restricted to pressure-based analyses and the associated creep behaviour. Viscoelastic materials exhibit additional constitutive time-dependent behaviours, determined by the stress and strain states, that are yet to be analysed in the context of volcanic ground deformation. By utilising a mechanically homogeneous model-space and distinct reservoir evolutions, we provide a comparison of three viscoelastic rheological models, including the commonly implemented Maxwell and Standard Linear Solid configurations, and their time-dependent behaviours from a fundamental perspective. We also investigate the differences between deformation timeseries resulting from a pressurisation or volume change; two contrasting approaches that are assumed to be equivalent through elastic modelling. Our results illustrate that the perceived influence of viscoelasticity is dependent on the mode of deformation, with stress-based pressurisation models imparting enhanced deformation relative to the elastic models, thus reducing pressure requirements. Strain-based volumetric models, however, exhibit reduced levels of deformation and may produce episodes of apparent ground subsidence induced by source inflation or vice versa, due to the relaxation of crustal stresses, dependent on whether the reservoir is modelled to be expanding or contracting, respectively.Natural Environment Research Council (NERC

Analisis Pendapatan Usahtani Wortel di Desa Netpala Kecamatan Mollo Utara, Kabupaten Timor Tengah Selatan

Penelitian mengenai Analisis Pendapatan Usahatani Wortel Di Desa Netpala Kecamatan Mollo Utara Kabupaten Timor Tengah Selatan. Pengumpulan Data dilaksanakan pada bulan bulan Maret 2018. Penelitian ini bertujuan untuk: (1) Mengetahui karateristik usahatani wortel. (2) mengetahui besar pendapatan yang diperoleh petani dari usahatani wortel. (3) Mengetahui besar keuntungan relatif yang diperoleh petani pada usahatani wortel. (4) mengetahui faktor-faktor yang mempengaruhi produksi usahatani wortel.  Metode pengumpulan data yang digunakan dalam penelitian ini adalah metode survei. Desa contoh ditentukan secara sengaja (purposive sampling), yakni Desa Netpala Kecamatan Mollo Utara Kabupaten Timor Tengah Selatan. Penentuan petani contoh, diambil dari populasi petani yang tergabung dalam 16 kelompok tani yaitu sebanyak 301 petani sehingga yang menjadi sample  sebanyak 75 petani contoh dengan penentuan per kelompok tani menggunakan metode Propotional Random Sampling. Hasil penelitian menunjukan bahwa karaterisik dari luas lahan yang dikelola1-5 are dengan jumlah petani sebanyak 19 orang, luas lahan 6-10 are sebanyak 32 orang, luas lahan 11-15 are sebanyak 10 orang dan luas lahan 16-20 are sebanyak 14 orang dan merupakan milik pribadi, benih yang digunakan oleh petani rata-rata 0,2 Kg dengan harga Rp.150.000 per Kg, pupuk yang digunakan merupakan pupuk bokasi, tahapan kegiatan usahatani meliputi: persiapan benih, persiapan lahan, penanaman, pemupukan, perawatan dan pasca panen. (2) besar pendapatan yang diperoleh petani dari usahatani wortel yaitu Rp. 289.147.179. (3) nilai R/C Rationya adalah 4,1 yang artinya usahatani wortel layak untuk diusahakan. (4) faktor luas lahan berpengaruh nyata terhadap produksi dari usahatani wortel sedangkan benih,pupuk dan tenaga kerja tidak berpengaruh nyata terhadap produksi dari usahatani wortel.  Kata kunci: usahatani wortel, pendapatan, fungsi produksi Cobb-Douglas  ABSTRACT Research on Carrot Revenue Market Analysis in Netpala Village, North Mollo District, South Central Timor District. Data Collection was held in March 2018. This study aims to: (1) identify the characteristics of carrot farming. (2)  analyze the income earned by farmers from carrot farming. (3) unserstand the relative profit gained by farmers in carrot farming. (4) deterine the factors which influence the production of carrot farming. Data collection method used in this research is a survey method. The choice of sample village is applied a purposive sampling technique. The chosen village is Netpala, located in the Sub District of Mollo Utara, South Central Timor District. Furthermore, to select the sample farmer or respondent with the number of 75 farmers is used a proportional random sampling, taken from the 301 farmers who are the emembers of 16 farmer groups. The results of data analysis showed that: (1) the carateristics of carrot farming operated by the farmers in research area as follow: the number of farmers operating the land with size of 1 – 5 acres consisted of 19 farmers, the number of farmers operating the land with size of 6-10 acres are 32 people, operated the land with size of 11-15 acres are 10 people, while those who operate the land with size of 16-20 acres are 14 people. The land operated totaly is holded personaly. Then the seed used by farmers on average is 0.2 kgs per farmer with the price of Rp.150,000 per kg, while the kind of fertilizer used is organic fertilizer, and the stages in farming activities include: seed preparation, land preparation, planting, fertilizing, maintenance and post-harvest. (2) the number of income earned by farmers from carrot farming are Rp. 289.147.179.  (3) the value of R / C Ratio is 4.1 which means carrot farming feasible to cultivate. (4) the size of land operated has a significant influence on the number of production of carrot farming, whereas the number of seeds, fertilizers and labors have no significant influence on  the number of production of carrot farming.  Key words: carrot farm, income, Cobb-Doulas production functio