اسلاید پاورپوینت: زلزله ای (seismic) ، تناوب (frequency) و اوزار (instrument)…

 

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نوع زبان : انگلیسی حجم : ۶٫۹۹ مگا بایت
نوع فایل : اسلاید پاورپوینت تعداد اسلایدها: ۲۹ صفحه
زمان استخراج مطلب : ۲۰۱۸/۱۱/۰۲ ۰۳:۳۷:۰۹ پسوند فایل : pptx

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این مطلب در تاریخ ۲۰۱۸/۱۱/۰۲ ۰۳:۳۷:۰۹ به صورت خودکار استخراج شده است. در صورت اعلام عدم رضایت تهیه کننده ی آن، طبق قوانین سایت از روی وب گاه حذف خواهد شد. همچنین این مطلب برگرفته از وب سایت زیر است و مسئولیت انتشار آن با منبع اصلی است.

https://www.tau.ac.il/~zivalon/seismology/Front/seismo10_seismometry.pptx

بخشی از محتوای متن استخراج شده از این فایل ppt

بخشی از محتوای متن استخراج شده از این فایل ppt

seismometry seismic networks instruments mainly based on shearer p.m. introduction to seismology cambridge university press ۱۹۹۹. lay t. and t.c. wallace modern global seismology academic press ۱۹۹۵. add us array and mems seismology seismic networks objectives the three main purposes are seismic alarm immediate response by civil defense seismic risk assessments hazard maps and building codes seismic monitoring incl. monitoring in volcanic regions nuclear explosions – international nuclear test ban treaty research – earth interior and earthquake source networks are described in terms of scope of investigations spatial resolution quality of data in terms of frequency content and dynamic range seismic networks frequency content and dynamic range the noise amplitude is of the order of nano meters whereas the signal amplitude is up to a few meters. thus the full dynamic range spans ۱ orders of magnitudes. seismic instruments the sensors the ۲ main sensor types are seismometers – weak motion accelerometers – strong motion seismometers are very sensitive to small and distant events and are thus too sensitive for strong motion signals. waveforms of the april ۴ ۲ ۱ mw ۷.۲ el mayor cucapah earthquake recorded at p۴۹۴. co located seismometer accelerometer and gps seismic instruments the sensors today s weak motion sensors are roughly divided into three categories the short period sp seismometers measure signals from approximately .۱ to ۱ hz with a corner frequency at ۱ hz. they have a flat response to ground velocity for frequencies greater than this corner frequency. the broadband sensors bb have a flat response to ground velocity from approximately . ۱ to ۵ hz. the very broadband seismometers vbb measure frequencies from below . ۱ hz to approximately ۱ hz. they are able to resolve earth s tides. seismic instruments the sensors since the measurements are done in a moving reference frame the earth’s surface almost all seismic sensors are based on the inertia of a suspended mass. the swinging system will have a resonance frequency seismic instruments the standard inertial seismometer these substitutions give this equation shows that the earth acceleration may be recovered by measuring the displacement of the mass and its time derivatives. seismic instruments the standard inertial seismometer it is convenient to define a resonant angular frequency and a dumping parameter as follows the stress balance equation of the inertial seismometer may be expressed in the frequency domain by considering harmonic earth displacement function of the form where is the angular frequency. similarly the displacement response of the seismometer mass can be expressed as and we have seismic instruments the standard inertial seismometer substituting these into the stress balance equation gives or were z w is the response function of the sensor. the response function is complex and may be expressed in polar form as where the amplitude the phase lag are real numbers. seismic instruments the standard inertial seismometer we obtained and the amplitude response falls off at frequencies below the resonant frequency and the ۱ hz sensor has little sensitivity at periods longer than ۵ s. for small damping a resonant peak occurs in the response spectrum near the seismometer natural resonance. seismic instruments the standard inertial seismometer we obtained and when the damping increases above ۱ the sensitivity decreases. seismic instruments the standard inertial seismometer we obtained and when h ۱ the system is said to be critically damped. seismometers generally perform optimally at values of damping close to critical. a polarity reversal at high frequencies. seismic instruments the standard inertial seismometer seismic instruments extending the filtering response seismic instruments extending the filtering response seismic instruments extending the filtering response seismic instruments extending the filtering response the above frequency response function relates the earth displacement u to the sensor mass displacement z. in the case of a seismometer that measures mass velocity dz dt the response function describes the sensor response to ground velocity du dt. in general seismometers may measure the displacement velocity or acceleration of the sensor mass and we may be interested in recovering the displacement velocity or acceleration of the ground. it is important to be aware of which combination is involved. each time derivative introduces a factor of −iω in the frequency domain. thus all other things being equal velocity and especially acceleration will be enriched in high frequencies relative to displacement. today purely mechanical sensors are only constructed to have resonance frequencies down to about ۱. hz short period sensors while sensors that can measure lower frequencies are based on the force balance fba principle of measuring acceleration directly. seismic instruments force balance principle fba a displacement transducer sends a current through a feedback coil through a resistor r in a negative feedback loop. feedback coil which can exert a force equal and opposite to the inertia force due to the largest acceleration we want to measure. the polarity of the current is such that it opposes any motion of the mass and it will try to prevent the mass from moving at all with respect to the frame. seismic instruments velocity response functions the original ida international deployment of accelerometers network was the first digital global seismic net work it uses gravimeters designed to record earth’s normal modes at very long periods and recorded one sample every ۱ s. data from the global digital seismo graph network gdsn began to become available in the late ۱۹۷ s. the gdsn long period channel recorded at one sample per second the gdsn short period channel recorded at ۲ samples per second. the gdsn response functions were designed to avoid the microseism noise peak at ۵ to ۸ s period see section ۱۱.۲ . broadband instruments began to be widely deployed in the late ۱۹۸ s and early ۱۹۹ s the broadband stations in the iris and geoscope networks have very wide frequency responses. seismic instruments impulse …

کلمات کلیدی پرکاربرد در این اسلاید پاورپوینت: زلزله ای (seismic), تناوب (frequency), اوزار (instrument), پاسخ برگشتی (response), ضبط کننده (sensor), جانشین سازی (displacement), خطوه (measure), توده (mass),

این فایل پاورپوینت شامل ۲۹  اسلاید و به زبان انگلیسی و حجم آن ۶٫۹۹ مگا بایت است. نوع قالب فایل pptx بوده که با این لینک قابل دانلود است. این مطلب برگرفته از سایت زیر است و مسئولیت انتشار آن با منبع اصلی می باشد که در تاریخ ۲۰۱۸/۱۱/۰۲ ۰۳:۳۷:۰۹ استخراج شده است.

https://www.tau.ac.il/~zivalon/seismology/Front/seismo10_seismometry.pptx

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